If you will unlock it with Ziphone it will DOWNGRADE your bootloader,and then if You will have problebs you will have to fiz it by yourself,Apple will not help you with it!
You just need to press jailbreak button.
Depends on what you want to do. If you want to use the official iPhone plan with the at&t service then you only need to jailbreak (to be able to add other apps).
If you already have a cingular/at&t contract ongoing and you want to use that sim card in the iphone (like me) then you probably will have to unlock and jailbreak.
Either way, your situation will be solved using "ziphone".
the reason why i want to unlocked my iphone is "i want to use this phone outside US and use their SIm Card, and also use my cingular and tmobile Sim Card here". more info please?
The problem is... that if you will use Ziphone it will downgrade your bootloader and its the BIG problem with Apple,they gonna say "we wont repair your iPhone" becaurse you downgraded your bootloader.... Thats a big matter! Which firmware are you running?(IMPORTANT)!