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 it? 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?