SIM card question

[och1975]

Obviously, I am a newbie here and just ordered an iPhone 3G 16G on ebay which was activated at an ATT store. I am a current ATT customer with a 3G SIM card in a Motorola phone with a data plan.

My question is, can I simply insert my existing SIM in the new iPhone and use my existing plan or will I need use a tool to unlock or jailbreak it? If so what software is recommended?

[fury]

The data plan most likely won't work. There is no known software unlock for the 3G, although I've heard that it's coming out at the end of the year. Additionally, even if you can get it to work as a phone with your SIM card, AT&T will know you're using an iPhone 3G on a non-iPhone plan, and will send you text messages and such warning you that you need to add an iPhone plan.

[och1975]

What exactly does the jailbreak software do then?

[dturner]

What exactly does the jailbreak software do then?
It allows you to put 3rd party apps on the phone such as themes,and other things a stock phone is not capable of.
This link (http://www.everythingicafe.com/forum/iphone-modifications/what-jailbreaking-is-and-how-to-do-it-27443.html) will give you a good overview of jailbreaking.