Cannot turn on 3G

Hi, I have an iPhone 3GS, and I have successfully unlocked it using Ultrasnow.

The thing is, everytime I turn on 3G, the phone just loses its signal completely. Is it because the unlock does not support 3G or have I done something wrong? If so, how do I remedy it?

Also, ever since the unlock, the "cellular data network" bit is gone, thus, can no longer change the APN, username and password for use on a different carrier.

Any ideas?

Thanks everyone!

What carrier are you using it on?

I have the some problem too, my iPhone 3gs was jailbroken with Redsn0w 0.8 and unlocked with Ultrasn0w 0.9. 2G network works perfectly, but The signal turns to "no service" as soon as I enable 3G.

I'm think of restoring it and redo the process again.
Btw, is it itune restore good enough to restore the iPhone back to the original state or I need to run some customized tools to re-virginize it.

Thanks!

iTunes restore is fine. Just make sure you set up as a new phone and don't then 'restore' a backup.