Did you update your iPhone's iOS after unlocking it.? If you have unlocked your iPhone using any temporary unlocking method, the iOS update would have re locked your iPhone to its previous network. To avoid this hassle, you need to unlock your iPhone using remote unlocking service. You can get the remote unlocking service for an iPhone from TheUnlockSpot.com This method of unlocking an iPhone is safe, simple, affordable, quick and permanent. It doesn't require a jailbreak too. Good luck.