From The iPhone Wiki
Hacktivation can be performed by most jailbreak tools that break the boot chain. Userland jailbreaks such as Spirit and Star cannot hacktivate, as they require interaction with programs that can only be used post-activation.
- Using redsn0w and not selecting any of the options. (This will work on any iPhone compatible with the version of redsn0w used but not A5+)
- If the iPhone is on 3.1 or 3.1.2, you can use blackra1n. (If you have an iPhone 3GS with the new bootrom it will be tethered.)
- Restore using a custom IPSW.
- By using a phonebook SIM card and connecting to iTunes and syncing the phone. (Note you must sync your phone for the activation token to be signed. If you put the phonebook SIM card in and take it out of the phone without syncing to iTunes, then it will go to the "Connect to iTunes/Emergency Call" screen.