If you already have a non-ATT sim in your iPhone, you iPhone will show as not active (emergency calls only) in itunes. Do not worry. Proceed with jailbreak using redsn0w. Redsn0w will activiate and jailbreak the iPHone 3g
'Redsn0w has stopped working'..this is the error I got while jailbreaking my iPhone 3g.
This problem is usually seen on vista computers. Follow these steps
1. Right click on redsn0w.exe -> go to properties -> go to 'compatibility' tab and select the 'run this program in compatibility mode for' and select Windows XP (Service pack 2)
2. Click apply and ok
3. Now right click on redsn0w.exe and click on 'Run as administrator'.
This will now work fine.