Switching iPhone 2G to a new account

I lost my AT&T iPhone 3GS last week, and as a replacement borrowed my friend's old 2G (also on AT&T).

I took it to an official AT&T store and they tried activating it with brand new SIM card, but they got the following error in iTunes:

The SIM card inserted in this iPhone does not appear to be supported.
Only compatible SIM cards from a supported carrier may be used to active the iPhone.
Please insert the SIM card that came with your iPhone or visit a supported Carrier's store to receive a replacement SIM card.

I was able to restore my 3GS back-up on the 2G phone, but only when using the old SIM card. The phone shows up in iTunes with my friend's phone number. When trying a new SIM card, I get the above error both at the AT&T and on my iMac at home.

I'm not sure if the phone is unlocked. Here are my questions:

• Does the phone need to be unlocked?
• Does my friend have to be at the store to unlock it, or can I ask them to do it?
• Can I unlock it myself with jailbreak software?
• Will unlocking it myself cause problems at the AT&T store?

HELP!

Quote:

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Originally Posted by petroleumjelliffe

I'm not sure if the phone is unlocked. Here are my questions:

• Does the phone need to be unlocked?
• Does my friend have to be at the store to unlock it, or can I ask them to do it?
• Can I unlock it myself with jailbreak software?
• Will unlocking it myself cause problems at the AT&T store?

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• It is not unlocked - the 2G iPhone behaves differently when swapping SIM cards to the 3G and 3GS.
• AT&T won't unlock it - ever. They refuse to support this. Lobby your local senator to push for regulations forcing carriers to unlock phones after their contract has expired.
• Yes you can jailbreak it and hacktivate it.
• It is quite likely that unofficial unlock or jailbreak/hacktivation will cause problems if you ever take the iPhone into the AT&T store. You can of course reverse the jailbreak and remove all trace before you take the iPhone into the store.