If this has happened with all three phones you have been given then it's a pretty sure bet that the problem isn't on the phone itself.
Does this happen with every call (ie. calls to landlines, other TM phones, other mobile phones)?
What's the greatest distance from your home that you have encountered the problem (ie. does it happen whatever tower you are connected to)?
Have you swapped your SIM card?
Have TM reset your line in an attempt to solve the problem?
Thanks for this information.
You didn't indicate how far you travel from home experiencing the same problem. What I'm trying to establish is whether the problem occurs on just one tower, because you never travel more than a short distance from home, or if you still get the problem when 10, 20 or more miles away?
There are several places that the problem might be being caused:
The phone itself - Unlikely because you have had the same problem on three different devices
The tower - We need to know about your traveling range to see if this might be the issue
The SIM card - If you have never had this swapped out by TM, it could be part of the problem
The configuration of your line - Doing a reset on your line isn't the same as doing a master reset on the phone. It can only be done by TM engineers. Again, if they haven't done this, it is a possible issue
When we have collected all this information together, you need to put it in an email to TForce@t-mobile.com, with your account details, so that they can look into this further.