you could try downloading "phone info" off the Play Store, it'll give you all your Samsung phones info I just tried it today ironass clued me into it
It may give you an idea...
you may also just contact your carrier and ask them.
Hmmmm.....
OK, your best bet is to pop a Sim card in from another carrier - say your phone is at&t, pop in a sprint Sim card, if it functions then your phone is unlocked - if it rejects it then your phone is locked to one carrier.