The Ultrasn0w 1.2 released by iPhone dev team for unlocking iPhone 3G and iPhone 3GS requires baseband update from 05.14 or 05.15 upwards to 06.15.00. For this the dev team is relying on iPad 3.2.2 firmware IPSW for extracting baseband 06.15.00 which works well on iPhone 3G/ 3GS making it unlock ready. Apple might withdraw the iPad 3.2.2 IPSW from their servers so here are some alternatives.
Download links for iPad 3.2.2 firmware IPSW :
Direct link from Apple – Download iPad 3.2.2 IPSW
Torrent link – Download iPad 3.2.2 IPSW