Really old AT&T SIM

[mjronline]

I have an AT&T plan that is grandfathered from about 5 years ago. It's an amazing plan that I don't want to change from. The SIM is from the old AT&T Wireless, before they switched to Cingular and then back to AT&T again. As it's an AT&T SIM, can I use it in a locked iPhone without having to jailbreak/unlock it? Also if I choose to unlock, do I also have to jailbreak? If I only unlock, will it cause issues with the 1.1.3 firmware?

Also without EDGE access or a specific iPhone plan, which features won't I be able to use on the iPhone? Can I still use "Locate Me" or "Google Maps"? Will I have issues with the "Visual Voicemail"? What else might I have problems with?

[southerndoc]

I don't think so. I think the iPhone uses its own SIM card (that has a marker in it to let the iPhone know it's an original iPhone SIM).

[EmAn]

I'm almost positive that the only way to get it to work is by unlocking.

[mjronline]

I'm almost positive that the only way to get it to work is by unlocking.

Ok, so is it possible to unlock it without also jailbreaking it? If I only unlock it, will I have any firmware issues with 1.1.3?