T-mobile problem calls cut off every 2 hours?

My t-mobile line keeps on cutting off during a call after every 2 hours exactly, can anyone help me get to the bottom of this p.s i did contact t-mobile they refreshed my network but still no luck may be its my phone i have an iphone 4.

Well you get what you pay for…

T-Mobile kinda sucks.
Switch to Verizon or At&t.