NO JOY Some PSTN calls to T-Mobile number disappear

routeunknown

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I’m trying to understand an unusual incoming-call failure involving my T-Mobile number. I’m hoping someone here has seen a similar problem, knows what causes it, or has experience porting an affected number to another carrier.


THE PROBLEM


Certain incoming calls disappear completely. My phone does not ring, nothing appears in Recents or Missed Calls, the call does not reach voicemail, and there is no notification or T-Mobile usage record. The caller may hear one ring before the call disconnects or goes nowhere.


The problem first affected calls from my employer’s corporate office. These calls previously reached this same number normally, gradually became intermittent, and now consistently fail.


My employer reportedly uses a T1 PRI through CenturyLink, and its IT department says the calls leave the company’s telephone system successfully.


CONTROLLED TESTING


The same corporate office can successfully call another T-Mobile number on my family account.


We also performed a physical SIM-swap test:


  1. My T-Mobile SIM was placed in another phone. Calls to my number still failed.
  2. The other T-Mobile SIM was placed in my phone. The corporate office successfully called that number.

Using the same originating office system and the same physical destination phone, calls to the other T-Mobile number complete while calls to my number fail. The problem follows my specific number or subscriber line rather than the phone.


T-Mobile replaced my physical SIM with a new eSIM and performed a network-side “Resend to Switch.” Neither fixed the problem. Phone settings, blocking, call forwarding, voicemail, Scam Shield, and other ordinary device-level causes have also been checked.


MORE THAN ONE ORIGINATING SYSTEM


This is no longer limited to my employer.


An unrelated business office recently called my number and experienced a similar failure: one ring from the caller’s perspective, followed by disconnection or no completion.


A T-Mobile support representative also attempted several scheduled callbacks. She could not reach me and said her calls terminated with “goodbye.”


Similar failures have therefore occurred from my employer’s corporate PRI, an unrelated business office, and T-Mobile’s support callback system. Personal mobile-originated calls may still complete, so the failure is selective rather than a total loss of incoming service.


Multiple support or engineering tickets have been opened. One ticket included the T-Mobile representative’s own failed callbacks but was reportedly canceled without resolution. I have now filed an informal FCC complaint.


WHAT I’M TRYING TO FIND OUT


  1. Has anyone seen a destination-number-specific failure like this, where calls from certain business or VoIP systems completely disappear but other calls still reach the same mobile number?
  2. If you have seen it, what caused it and how was it ultimately fixed?
  3. Has anyone ported the same affected number from T-Mobile to Verizon or another carrier? Did porting that number stop the incoming-call failures?

My main concern is whether this problem exists within T-Mobile’s routing or subscriber systems and would disappear after porting, or whether a number-specific routing problem could follow the number to Verizon.


I am especially interested in experience involving the same malfunctioning number—not cases where the customer abandoned the number and obtained a new one.

Thanks!
 
I saw a situation were some calls were not going through. After looking up which provider held the numbers, they were all Verizon. Only could do then was to contact upstream to put in a ticket.
 
I saw a situation were some calls were not going through. After looking up which provider held the numbers, they were all Verizon. Only could do then was to contact upstream to put in a ticket.
Thank you for your response. I have T-mobile service and have a ticket in with them. some of the calls I’m not receiving are from T1 PRI through CenturyLink. I can’t receive calls from my dentist office or my sisters office either and who knows what other calls I’m missing.
 
Sounds STIR/SHAKEN related especially if your employer is still utilizing a PRI/T1 line and doesn't pass STIR/SHAKEN Certification/credentials. The cellular carriers are getting, dare I say, brutal at all out blocking calls the are attested at C. If you have any spam filtering control your T-Mobile account, even if you're not using an app, check and add the number to your white list and see if the calls come though. As others have said your employer should enter a ticket with their provider with call examples to find out why calls are not terminating.
I believe I also heard that Lumen/CenturyLink/Level-3 is discontinuing voice services that may have something to do with it as well.
 
I believe I also heard that Lumen/CenturyLink/Level-3 is discontinuing voice services that may have something to do with it as well.
The voice services are End of Sale not End of Life/Service. While there's no planned timeline for this all current contracts are going to be honored and roll to month-to-month after they expire until Lumen comes up with an End of Service timetable to actually turn it off. So Lumen is no longer selling voice services but they aren't turning voice services off.
 
The cellular carriers are getting, dare I say, brutal at all out blocking calls the are attested at C
No carrier is using the attestation level alone. B/C levels just add more flags and cause checks faster but there is a combination of the STIR/SHAKEN data which includes not only the attestation but the origination carrier information. That is also used in the logic of checking the call profile of the originating carrier. A call with an Attestation of C still might be allowed due to the calling profile of the carrier (i.e. clean history with fraud, etc) while a call with an Attestation of A could be blocked because the calling profile of the carrier is dirty.

For example, Neutral Tandem has a long reputation for providing services to high volume auto dialer companies. All those calls would present an Attestation of A but because Neutral Tandem has an extremely dirty calling profile history those A level calls have a very high chance (and often are) marked as "Likely SPAM" or blocked outright.

Again, the levels of A, B and C are just one data point used in a multi-data point check against not just the number but the origination carrier and call history profiles of both.
 
Sounds STIR/SHAKEN related especially if your employer is still utilizing a PRI/T1 line and doesn't pass STIR/SHAKEN Certification/credentials. The cellular carriers are getting, dare I say, brutal at all out blocking calls the are attested at C. If you have any spam filtering control your T-Mobile account, even if you're not using an app, check and add the number to your white list and see if the calls come though. As others have said your employer should enter a ticket with their provider with call examples to find out why calls are not terminating.
I believe I also heard that Lumen/CenturyLink/Level-3 is discontinuing voice services that may have something to do with it as well.

Thanks — this helps. One additional detail: Scam Shield/Scam Block is not enabled on my line, and T-Mobile has already whitelisted the known originating numbers. That made no difference.

What I’m trying to understand is whether STIR/SHAKEN really fits the overall pattern, because the failures are no longer isolated to my employer’s PRI/T1.

I’ve now had the same type of failure from an unrelated business in a different location, and a T-Mobile support representative has also been unable to complete a call to my number.

The failure also follows my line/number, not the handset. When we swapped SIMs between two T-Mobile phones, my line still failed in the other phone, while the other T-Mobile line successfully received the employer calls in my phone.

These calls also historically worked to my number, became intermittent over time, and then stopped. I have older successful calls from the same employer numbers in my T-Mobile call records.

So my main question is: Does STIR/SHAKEN still make sense as the likely explanation when multiple unrelated originating sources are failing specifically to one destination number, while another T-Mobile number can receive the same calls?

Or would that pattern make you suspect something associated with the routing/provisioning or treatment of the destination number itself?

Unfortunately, T-Mobile has declined my request to perform a live trace, so I’m trying to determine what the existing evidence most strongly points to.
 
Its too bad T-Mobile will not doa live trace that would probably find the issue right away. Since other calls are also failing that may take STIR/SHAKEN out of the discussion. It would appear to be a routing or provisioning issue with the line. Your employer should open a ticket with Century Link with call examples for investigation.
 
If T-Mobile is uncooperative, port to Verizon or another carrier
 
Its too bad T-Mobile will not doa live trace that would probably find the issue right away. Since other calls are also failing that may take STIR/SHAKEN out of the discussion. It would appear to be a routing or provisioning issue with the line. Your employer should open a ticket with Century Link with call examples for investigation.
Thank you, I’m going to have my have my employer open a ticket with Century Link.
 
Assuming that there is one nearby, stop by a T-Mobile store and ask them to diagnose and fix your routing issue. Even if the local staff is not successful they have access to back office technical people who can help. That's one thing I like about their stores.
 
Assuming that there is one nearby, stop by a T-Mobile store and ask them to diagnose and fix your routing issue. Even if the local staff is not successful they have access to back office technical people who can help. That's one thing I like about their stores.
Thanks, I have an open ticket with T-mobile tech support but an in person visit might be helpful.
 
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