Can I use a normal att plan on the iphone 3g?

HI whether you want to use the iphone 3g with your AT&T service then you must first check that whether the iphone 3g is unlocked or locked with AT&T already else if the iphone is locked to some other network provider then it wont accept your AT&T sim until you unlock it ..You can easily unlock the iphone 3g through online providers like Unlocking4U.com here they are rendering remote unlocking service to unlock all model iphone from network provider .You first check that whether the service is available for your country and network provider .If yes then pay for it and unlock your iphone 3g then freely use it with any GSM sim ...