iPhone Updating jailbroken iPhone 3G

you can't brick it, download firmwarm from http://www.felixbruns.de/iPod/firmware/ I believe 4.2.1 is the last one. I clarified has tutorials for rejailbreaking etc.http://www.iclarified.com/jailbreak/

4.2.1 is the latest version for the iPhone 3G, but 3.1.3 runs much quicker if you don't need iOS 4 or above to run a certain app.

To get to 4.2.1 just plug your phone into your computer and hit 'Update' in iTunes.

Make sure you aren't using a software unlock before upgrading. You will lose your software unlockable (with ultrasn0w) baseband if you upgrade to stock 4.2.1.

Hi There, I recently JB my iPhone 3G
Firmware: 4.2.1
Baseband: 05.15.04-5.8

Cydia is installed wifi functioning sim detected but constantly searching. I suppose this is normal for a unsupported sim...

After a bit of reading the iPad Baseband gets the phone unlocked but you lose GPS functionality. most of the posts about this are dated 2010/2011. So I am just looking to clarify.

From what I have gathered there is now a downgrade option from the iPad baseband? I have used the latest version of RS available (afaik) v0.9.15b3

All that is left is to upgrade to iPad BB and downgrade?
I would like the phone unlocked and gps functioning properly.

Since your phone is older, I would consider going through AT&T directly for an iPhone unlock (no charge). They unlock older iPhones that we're in good standing. I did that with my iPhone 3G. Google it, and you can do it online.

Hi Thanks for the Reply! wish it was that simple lol@AT&T,

It's locked to AU/vodaphone so not sure how US/AT&T could help. would be nice though.

Anyway, doesn't seem like the baseband gets updated at all even when the option is ticked. JB/Activate worked fine though ^^

Trying this https://forums.macrumors.com/threads/1482885/

--- Update #1
Older version of RS worked tried v0.9.6b6 - Worked first time. Attempting the downgrade baseband for unlock now.

--- Update #2
RS0.9.15b3 BB Downgrade left me with Blank IMEI,BB! lol shouldn't the latest software work the best??(Not in this case it appears) Have to say I was a bit concerned but also well informed that this could be an eventual outcome (Expensive iPod lol)

--- Update #3
Okay well After a bit of Research. Here is the approach which worked for me.
1. JB/Activate 05.15 BB (locked) with RS0.9.15b3
2. Install iPad 06.15 BB with RS0.9.6b6
3. Downgrade to 05.13 BB with RS0.9.14b2
4. Install UltraSn0w 1.2.7 with Cydia. Unlocked!

Thanks Guys!
Credits: iphone dev-team, dhlizard, TriJetHero & the Friendly macrumors Community ^^