If you bought an iPhone 4 and will be your first time activating, here's a thing you might to read: There are 2 kinds of Iphone 4's in the USA, one that is bought through Apple and one that is bought through another party like AT&T or Bestbuy. The iPhone 4's that come direct from any Apple store are locked to the original account holders ID (SS# etc), the other kind are not locked in the same way. So if you bought an iPhone 4 that was purchased from ATT or Bestbuy it would be easier to activate and can be use with any ATT sim card. If your iPhone was purchased through Apple, you might want to consider buying a special "phonebook sim card" called "DITS". Here's a thread I started regarding this issue: http://forums.macrumors.com/showthread.php?t=971636&highlight=swoosh0217 Sorry for reposting.