From your original post, what I think you have set right now is the VMX Locator, where if you do not answer your phone, the system says something to the effect of:
He is not available right now, to call an operator dial Zero, to reach him on an alternate number (cell) dial 1.
what I THINK you want is not the VMX locator, nor is it the No Answer setting on the bottom of the FollowMe section where if you don't answer THAT it goes to Voicemail or (what you want is an IVR)
So, I THINK what you really want is at the very bottom of the Advanced tab of the extensions settings page:
Here there are three options:
What to do if you don't answer - not at your desk -- This is what I think you want to set to your IVR.
What to do if you are busy -- on the phone already, maybe a voicemail here so you can call them back when you are free.
What to do if your extension becomes unreachable (deregisters - A force FollowMe to your cell would be good here.
This is a good setup unless your entire system crashes, then what you should see if is available from your DID provider is a FailOver option if the trunk can't reach your system at all, Fail over to a cell phone on Main number -- or to different people (one being your main IT guy/Gal) if you have many numbers that sends out your OWN number as the callerID.
By the OP this is what I think you are looking to do.