Service problems with T-Mobile and other carriers, iPhone 3G 3.1.2

[Jamesfschwartz]

Earlier this year I bought an iPhone 3G, had it jailbroken and unlocked. I've had problems ever since with all the SIM cards I've tried (T-Mobile, Telcel, Movistar, etc.)

Upon inserting the SIM card, It will show the carrier and some bars, but usually within 10 seconds or so I'll receive the "Network Lost" tab and it will show "No Service". Then, say I switch it back on in 5 minutes, it will have service, but within 5-10 seconds of doing so (if I don't make a call quickly) I'll lose it. It has been the same for quite a while now. I am in a well-covered area, so that couldn't be the issue.

iPhone: 3G 8GB, 3.1.2
Jailbreak & Unlock: Blackra1n, Sn0w

What I've done:

• Reset the network settings
• Switched onto "Airplane Mode" and off
• Tried with the "Enable 3G" tab on and off
• Reset data settings
• Shut off, and rebooted

So far, I've had no luck, and have just been surviving with it as it is. It's a gigantic annoyance though, and I'd LOVE to be able to fix it. An answer or possible solutions would be greatly appreciated.

[babyblue_pimp]

Alot of people have had this issue with Blacksn0w. I'd recommend upgrading to 4.0 and using ultrasn0w to unlock. 4.0 will update your baseband, and ultrasn0w will reunlock it.

[Jamesfschwartz]

Okay, I'll give that a go. Could you give me an address where I can download 4.0?