Can I use a Cingular SIM card when jailbreaking?

[jlconlin]

I don't have an AT&T SIM card so I have been unable to upgrade my 3GS to 4.0 yet. My friend gave me his old Cingular SIM card. Will that work? I'm worried about updating my phone and then not getting it to work. I am on T-Mobile.

Thanks,
Jeremy

[neodude237]

I (think) it might work, what are you trying to use it for? It may not work to make calls or whatever, but if you are trying to bypass activation, I think it will.

[jlconlin]

I just need a SIM card so the phone will work until I get to jailbreakme.com With just a T-Mobile SIM card, I won't be able to do anything with my phone. I'm hoping this old Cingular card will work.

Jeremy