How to: Use an old Cingular SIM with the iPhone

Just yesterday, we reported that an enterprising group of hackers had successfully modified the iPhone OS so it would support old AT&T/Cingular SIM cards--including cards for corporate accounts. Well, in only a few short hours, some kind soul has created a step-by-step FAQ (with screenshots!) for anyone with an existing Cingular/AT&T plan who would rather not sign up for another 2-year service plan.