I purchased an unlocked for t mobile iPhone 3GS on eBay, here's all the info I have:

iPhone 3GS
Firmware: Jailbroken 4.2.1
Baseband: 06.15.00
iOS History: 3.1.3, 4.0, 4.0.1, 4.1, 4.2.1
iOS Never Used: 4.0.2
Jailbreak History: 4.0.1, 4.1, 4.2.1
Jailbreak Tools: Jailbreakme.com
GreenPois0n RC3, RC6
Redsn0w 0.9.6 Beta 5
SHSH Saved: 4.0, 4.0.1, 4.1, 4.2 Beta 3,
4.2.1, 4.3
SHSH Tools: TinyUmbrella 4.30.04

So the issue I'm running into is the phone keeps jumping in and out of service/no service. Yesterday i had service all day, no issues. I woke up this am and the phone had no service at all. I've had it since Friday of last week and the issue just continues to come and go. Is there any help anyone can offer?

I used a BB Curve previously and also got a new SIM, thinking maybe that was the problem. However it continues to happen.

3G is off, and I've tried to reset network settings.

Thanks to anyone who can help!