I have the bold 9700 and the curve 8320 before that and both phone had the same problem. When connected to WIFI anyhere and the phone is using UMA to make calls the call go silent on my end but are live and the people can here me on the other end. I heve spoken to Tmobile and apparently it a problem on there end and there is a master case # for this problem that has been ongoing since september 2009. The tmobile Reps that i have spoken to the ones with knowledge have no idea when the issue will be resolved. I'm curios if anyone has any light to shed on the situation. I will supply the master case # later when i have access to it.
I have this often. The silent time you mentioned usually matches when my 8520 shifts between UMA & EDGE. The TMO BB Rep told me to disable one or the other to prevent dropped calls but they dropped anyway with signal varience on both transports. You are NOT alone.
T-Mobile UMA phone call connection Problem
