[dkchunky]

OK, I’ve JB and unlocked my iPhone 3.0 for T-mobile. Got the data working, but still can’t get applications to work. All the 3rd party apps will not work at all. The app icon shows up in my home screen, but when I click on one…it fails to launch and returns me to the home screen. Can someone help?

[ComputerQueen]

The only solution I am aware of is to re-jailbreak and reload. My grandson uploaded an app that caused Cydia to not load....would act like it's starting and just goes back to home screen.

To jailbreak - always start with a "fresh" restore - like your iphone is just out of the box - even if you are on the same firmware....always do a FRESH restore....it seems to eliminate a lot of issues going forward.

The only way we found to get it to work correctly was to rejailbreak and unlock again. Before using Ultrasn0w, I believe for T-Mobile you need to turn 3G off. (I think that is just for unlocking initially).

Steps...(assuming you are using a 3G and PC)
Back up your phone in itunes (if possible)
Put phone in DFU mode
Restore with 3.0.1 - keeping phone plugged in and itunes open...
After restored and iTUnes recognizes phone and asks you if you want to restore from backup or set up new phone - Canx out of iTunes
Jailbreak with redsn0w 0.7.2 if using XP Pro - and select firmware file of 3.0 NOT 3.0.1
After jailbreak, load Cydia (and don't load ICY) and add repo666.ultrasn0w.com to Sources and then install ultrasn0w.

You can have the sim card out of the phone for the above process.

After above is done successfully, go to iTunes and restore from Backup to reload you files.

Lobby0ne has a sticky in Jailbreaking Iphone forum detailing above steps.
Good Luck.