Dialpad / SIM wont keep open

I have an issue iPhone 3G / Yellowsn0w



I JailBreak my iPhone, and it works well with a Pre-Paid SIM card.
I recently sold it to my friend, and he wants to use a "contract" SIM in the phone.


When everything works well with the iPhone, 3G, Wifi, Recieve calls, Send and reciever SMS.

... But every time he tries to click on the phone buttom (to manualy make a call), the dial pad comes up for 2 seconds, and then it closes on him!


What can be the issue here?

Current stat's of the iPhone
Software version: 2.2 (5G77)
Modem Firmware: 2.28.00


Has a few app's installed.

Poof - Cydelet - Cycorder - Qik - iPref -
and some other apps, to numerous to mention.