Motorola CLIQ :: Phone Automatically Restarts Itself

I recently bought an unlocked T-Mobile CLIQ and I'm using it in Canada (FIDO). I have 2 SIM cards that I've been testing with the CLIQ. On one phone SIM, the phone works perfectly fine no complaints (in fact, its quite a good phone). However, on my 2nd SIM card, the phone has problems picking up a signal, so it spends most of its time on Emergency Call Only and then to add insult to injury, the phone will automatically restart after several minutes. I have a hard time believing that a SIM card can cause this phone to mess up but I can't explain how it works for one SIM, but not for another?