Bought used phone, how to restore to 3.0?

[applesucksbad]

Hey guys, first post, first iPhone!

I just bought a phone from craigslist from a guy. It has 3.0 on it right now. I need to unlock it to use with an AT&T sim with no data. How far should I upgrade the firmware (if any?). What firmware allows the highest flexibility? I'd like to restore it at least as it still have a bunch of his stuff on it.

I tried upgrading to 3.1.3, but apparently it's unsigned by apple now, I can't find any clear guide on how to do it.

Also, the phone is jailbroken, but cydia quits on startup. Thanks!

 

[Myzhi]

Since phone is already pwned JB:

1) Create (pwnagetool) or find (google) a custom already JB firmware file (one that keeps the baseband) you wish upgrade to. Restore with that file through iTunes.

2) On the phone, use Cydia to install Ultrasnow = unlock.

And, ATT will automatically add a data plan once they see it's an iPhone due to the phone's IMEI . Unlocking doesn't stop them from seeing the IMEI, but it does allow you to use Tmobile without data plan.

 

[applesucksbad]

Wow, thanks for the tip, in all the time I was researching how to use an iPhone with no data, no one pointed this out to me. Thanks for the warning. Time to ebay the phone I guess.