Just bought an iPhone 1.1.2 OTB for christmas for my mom. I already have an account with AT&T and want to use the same sim card. I've already managed to get it jailbroken and what not...but i can't get any service. What else needs to be done?

Sorry if this has already been asked and then answered, I just haven't found a definite response yet, there's a lot of posts.

Thanks!