NO JOY T-Mobile Conditional Call Forwarding to VoIP DID Fails - Seeking Workarounds

[sandiegopbx]

Hi everyone,

I'm hoping to get some advice or hear about others' experiences with a specific call forwarding issue I'm facing with T-Mobile.

I want to use my new FreePBX server as a call screener for my T-Mobile cell phone. The plan is to use Conditional Call Forwarding (*004*...) and/or Unconditional (**21* ...) to send declined/unanswered calls from my T-Mobile number to a dedicated DID on my PBX, which then runs a "press 1 to connect" IVR to filter out spam.

My FreePBX server is 100% functional. Calling the VoIP DID for the screener directly works perfectly every time.Conditional Call Forwarding on my T-Mobile line itself is working. I've successfully tested forwarding my number to another T-Mobile number, and it works flawlessly.

The Problem:

When I set the conditional forward destination to my VoIP DID (from BulkVS), the forward fails. The phone status shows "Voice forwarded" yet any declined or unanswered call just keeps ringing or will hit a slow busy signal after 20 seconds and then drop. It never reaches my server (confirmed in shell).

This definitively points to an issue where T-Mobile's network is unable or unwilling to complete the forward to my specific VoIP DID. It seems to be a carrier-level block or routing problem.

My Questions:

1. Has anyone successfully implemented this kind of T-Mobile -> VoIP DID forwarding recently?
2. Is this a known T-Mobile block? Are there specific types of VoIP DIDs (e.g., from certain carriers like CallCentric, VoIP.ms, Twilio) that are known to work better for this?
3. If direct forwarding is no longer viable, what is the best "intermediary" or "bridge" service that you are using today? (e.g., Forwarding to a Google Voice number that then SIP forwards to the PBX, etc.)

I'm ready to call T-Mobile support, but I wanted to get some insight from the community first to see if there's a known workaround before I spend hours on the phone with them.

Thanks for sharing your wisdom!

 

[Halea]

I have an old prepaid T-Mobile phone in my car which is on call forwarding most of the time and I never had an issue getting the calls onto BulkVS DIDs.
Only, I use the *21*123456789# format. Maybe the problem is with the **21 format. I know those formats mushroomed recently and there are many different ways of doing it.
I don't think that the issue is either with Tmobile or BulkVS. If there is a routing issue it's probably with the NPA-NXX pair of the DID which is too new or too peculiar and it's not being properly handled by the various switches involved. It happened to me more than once that newly created such pairs were not reachable from some networks. After a while the problem was fixed by the carriers.

 

[sandiegopbx]

Thank you so much for this incredibly helpful reply. This is exactly the kind of real-world experience I was hoping to find.

Your message gives me hope, as it confirms that T-Mobile and BulkVS can work together for call forwarding.

I tried your suggestion of using Unconditional Forwarding (*21*...#) to my BulkVS DID, but unfortunately, I'm still getting the same result: my phone shows "Voice forwarded" correctly but the call fails to connect to my PBX.

You made an excellent point about the possibility of the DID's NPA-NXX being too new. I have no idea if my DID is a new number or not, but that could explain it.

Do you know how to tell the difference between a typical or unusual prefix in your experience? But I suppose this is the most likely cause now. If this is a routing table propagation issue, is the only solution to just wait, or would getting a different DID from a more established number block from BulkVS likely solve it immediately? If so, how can I tell which would be a good number to use?

Thanks again for your fantastic insight!

 

[krzykat]

I have T-Mobile, and do almost this exactly. My reasoning is that I much prefer my own voicemail system with transcription to email over what T-Mobile or others offer. I have one little thing different that I do that I think is worthwhile to some. I use BulkVS - but for this setup, I'm using a different carrier, but if I have time, I could try that as well. Something that I've done that I LOVE and I've had clients ask me to setup for them is that often people find their desk phone better to talk on than their mobile, might be speakerphone or a great Sennheiser headset, plus you could have all your calls directed to that DID recorded. So what I do - is I do the conditional forwarding, and then I ring my desk phone for just a few seconds before it hits my voicemail. This gives me my cake and eat it too. So if a call comes in that I want to take on my mobile, but I'm at my desk, I'll just decline it on phone, and answer at desk. I've also had times when my mobile just doesn't have a signal. On to the main part of your question. My notes show the way to send the calls are to use all these options:

• Forward when busy / call declined
  Dial: **67*destination-number#
• Forward when no answer
  Dial: **61*destination-number#
• Forward when unreachable / phone off
  Dial: **62*destination-number#

 

[sandiegopbx]

Wow, thank you for this incredibly detailed and insightful response. The workflow you've described is absolutely brilliant... it's not just a solution, it's a complete productivity system.

The "decline on mobile to answer at desk" strategy is a game-changer, and it's exactly the kind of powerful, seamless integration I'm trying to achieve with my new PBX. Your setup is my new blueprint for the perfect personal call flow.

Thank you also for breaking down the individual conditional forwarding codes (**61*, **67*, etc.). I had been using the all-in-one *004* code, and it's good to know how to control them individually.

I have one crucial follow-up question, as it seems to be the final hurdle I'm facing. When I try to set any of these conditional forwards to my VoIP DID from BulkVS, my T-Mobile phone shows a "Voice forwarded" status, but the forward doesn't actually work.

Did you run into any issues with T-Mobile initially accepting your VoIP DID as a valid forwarding number? It seems like my T-Mobile account is actively blocking the forward to that specific type of number, even though forwarding to another mobile number works perfectly.

It's encouraging to know that you've made this work with a different carrier. Who did you use?

Any insight you have into getting T-Mobile to "play ball" with the VoIP DID would be the final piece of my puzzle.

Thank you again for sharing your incredible setup!

 

[krzykat]

Wow, thank you for this incredibly detailed and insightful response. The workflow you've described is absolutely brilliant... it's not just a solution, it's a complete productivity system.

The "decline on mobile to answer at desk" strategy is a game-changer, and it's exactly the kind of powerful, seamless integration I'm trying to achieve with my new PBX. Your setup is my new blueprint for the perfect personal call flow.

Thank you also for breaking down the individual conditional forwarding codes (**61*, **67*, etc.). I had been using the all-in-one *004* code, and it's good to know how to control them individually.

I have one crucial follow-up question, as it seems to be the final hurdle I'm facing. When I try to set any of these conditional forwards to my VoIP DID from BulkVS, my T-Mobile phone shows a "Voice forwarded" status, but the forward doesn't actually work.

Did you run into any issues with T-Mobile initially accepting your VoIP DID as a valid forwarding number? It seems like my T-Mobile account is actively blocking the forward to that specific type of number, even though forwarding to another mobile number works perfectly.

It's encouraging to know that you've made this work with a different carrier. Who did you use?

Any insight you have into getting T-Mobile to "play ball" with the VoIP DID would be the final piece of my puzzle.

Thank you again for sharing your incredible setup!

No - T-Mobile should be completely dumb with regards to it. If you look at details, you will find that the no-answer forward employed by your phone just sends it to a different DID (owned by T-Mobile) - you're now just sending it to another DID (owned by you). I mean let's put it this way, it doesn't know or care if you're forwarding to a VoIP line, your home phone number, or the white house. I don't have an IVR on entry, but that would be doable. If you wanted to get crazy, I think someone on here, maybe Ward at one time had a script whereby it would look up in database to see if that phone number was answered before and if so, would allow the call through. If not, it would do a simple IVR something like "If you're a human, press 1" - it will evade most telemarketers and such - and that way you only inconvenience someone once.

Back to your question/issue. T-Mobile valid forwarding ... should NOT be an issue.

 

[sandiegopbx]

Thank you again. Your confidence that T-Mobile shouldn't be blocking the DID is the single most helpful piece of information I've received. It moves my troubleshooting away from a policy issue and squarely into a technical routing problem.

I believe you and the other poster are right: the issue must be that T-Mobile's network switches can't find a valid route to the specific NPA-NXX of my brand new BulkVS DID. It explains why a direct call works, but a forwarded call from T-Mobile's network fails.

The "check a database and challenge first-time callers" script you described is exactly the system I'm trying to build! It sounds incredible, and it's great to have confirmation that this is the right path. I"ll have to try to find that script.

You mentioned that for this specific setup, you are using a different carrier than BulkVS. This might be the final clue. Could you share which VoIP provider you are using for the DID that T-Mobile is successfully forwarding to?

It's possible their number blocks are more established and have better route propagation across all carriers. If so, my simplest solution would be to get a new DID for this purpose from a provider that is known to work with T-Mobile forwarding.

Thank you for sharing your time and expertise.

 

[krzykat]

FYI - on my Android phone, under "Call Forwarding" - it shows:
Forward when busy: Forward calls to +<my11digitDID>
Forward when unanswered: <SAME>
Forward when unreachable: <SAME>

You're sure your DID works fine? What happens when you dial it from your mobile? Does it act as expected? In your routing, just have the inbound DID, do NOT put anything in CID unless you want to limit who gets in.

 

[krzykat]

You mentioned that for this specific setup, you are using a different carrier than BulkVS. This might be the final clue. Could you share which VoIP provider you are using for the DID that T-Mobile is successfully forwarding to?

It's possible their number blocks are more established and have better route propagation across all carriers. If so, my simplest solution would be to get a new DID for this purpose from a provider that is known to work with T-Mobile forwarding.

That was with Skyetel, but I would bet that's not the issue. If you want to check routing of T-Mobile across, just dial the number from your mobile. Make sure your trunk is set right. Depending on what CID / Network is calling, I've seen BVS route it on a different IP. If its a brand new DID you just bought - try another - they're cheap - and easy. If you have a BVS DID going onto your PBX that does work - even though not made for your VM setup, just do forwarding to there for testing to rule things out.

 

[sandiegopbx]

I performed the "Known-Good DID" test. Here’s what I did:

1. I confirmed again that my DID#1 and my DID#2 both work perfectly when called directly from any phone. They both route to their respective IVRs on my PBX without issue.
2. I then set up Conditional Call Forwarding on my T-Mobile line to forward declined calls to my established DID#2.

The Bizarre Result:
When I call my T-Mobile line from a separate outside number and decline it, that call gets presented back to my T-Mobile phone again, creating a feedback loop where my phone shows a new call coming in from my outside number. It just keeps going like that.

Also, my T-Mobile number is absolutely not in any Ring Group or Find Me/Follow Me list on my PBX. My only "real" endpoints are SIP softphones.

I feel like this must be an NPA-NXX routing issue. It seems T-Mobile's forward to my DID's fail. Both purchased a BulkVS.

As a final test before trying another provider, I'm going to follow your advice to try another DID from BulkVS. I'll purchase one from a completely different prefix (a different NPA-NXX) and see if T-Mobile can forward to it cleanly without a routing failure or this strange loop. It's a very cheap test and seems like the next logical step.

I'll report back with the results. Thank you again for being so generous with your time and expertise! This has been an incredible learning experience.

 

[sandiegopbx]

SOLUTION:

Purchased a DID with CallCentric and it worked immediately

 

[krzykat]

SOLUTION:

Purchased a DID with CallCentric and it worked immediately

Interesting. My guess is that you got a bad DID. Sometimes depending on where the DID came from, a carrier such as T-Mobile doesn't have the proper routing table. That's why I asked you to call the number directly from your T-Mobile phone. I have MANY Bulk-VS DID's, so within the next few days, I'll try to move my VM to a bulkVS DID and see how that works. I'll be very surprised if it does, and if not, I'll be speaking with BulkVS about that.

 

[Samot]

Have you actually looked at logs or run the logger to see if the call is hitting the PBX and being rejected or accepted? Kind of sounds like the only thing done was making a call and just going off that.

 

[sandiegopbx]

Interesting. My guess is that you got a bad DID. Sometimes depending on where the DID came from, a carrier such as T-Mobile doesn't have the proper routing table. That's why I asked you to call the number directly from your T-Mobile phone. I have MANY Bulk-VS DID's, so within the next few days, I'll try to move my VM to a bulkVS DID and see how that works. I'll be very surprised if it does, and if not, I'll be speaking with BulkVS about that.

Correct, I called the number directly from my T-Mobile phone, there was no issue. Hit my IVR every time.

As soon as I tried other numbers than ones I had purchased from BulkVS, it worked.

 

[sandiegopbx]

Have you actually looked at logs or run the logger to see if the call is hitting the PBX and being rejected or accepted? Kind of sounds like the only thing done was making a call and just going off that.

I was watching in real-time. My call never hit the IVR, period.

Using a Callcentric New York DID did work, however.

 

[kenn10]

I think the issue lies with T-Mobile's robust spam blocking technology I have BulkVS DIDs and have never experienced issues with forwarded calls to/from my cell phone or through the PBX. Phone numbers are taken and released continually without a "rest period" like the phone companies used to implement. A scam artist can pick numbers, use them for a day or two and then dump them when they start getting blocked. You might pick up one of those numbers the next day and have issues.

 

[Halea]

If you think you've investigated the issue long and deep enough, and the problem is pointing to the DID purchased from BulkVS, just contact their technical support. That's another company with good and competent support people. They will get to the bottom of it if their network or their upstream is the source of the problem.
If the number is blacklisted entirely or partially on one or more networks their upstream will be able to figure out. The numbers blacklisted for abuse are tracked.

 

[sandiegopbx]

Good idea, I'll contact BulkVS, will let you know what happens!