how to flash a iphone 3 to metro?

Flashing is for CDMA phones.If you have GSM network based phone means no need to flash your phone,Unlocking is enough for swap your network carrier to metro.For unlocking visit SuperUnlockCodes.com Here you can unlock your iphone 3 by Remote unlocking method.It's one of the best and safe way to unlock your iphone without jailbreaking.