IPhone Unlock MC603B No Service

Are you sure it was factory unlocked?  If it was software unlocked then the phone will automatically lock again after you restore or update.  This shouldn't happen if it came unlocked in the first place.  Try calling apple care, they will be able to tell you if the phone is locked or if there is a different problem you should address.  But keep in mind that apple does not unlock phones and they cannot tell you which carrier has the phone locked.  They will only tell you if the phone is actually factory unlocked or locked.

If that model # is accurate, then this is a UK, United Kingdom iPhone of any carrier there, ie O2, Tesco, Vodafone, Orange, T-Mobile, 3. If Anne is correct and Apple tells you that the iPhone is locked, then contact these Carriers for help.

yes it was unlocked because i upgraded 2 times from 4.3.3 to 4.3.5 and from 4.3.5 to 5.0.1 and no problems found

but when i tried to upgrade from 5.0.1 to 5.1.1

the lock happened

Toggle ON/OFF Airplane Mode, leave it OFF. Reset Network Settings, tap Settings App>General>Reset>Reset Network Settings. Try another SIM Card. Restore again with iTunes on computer.

i tried that but not working