Yes, you can put any SIM card into any unlocked phone. Any phone that has been bought here, weither it be pay as you go, or on a plan is unlocked. HOWEVER, the ones from the states are not unlocked, unless you unlock them or get them unlocked. But, after you unlock them, you can put any SIM card in it you wish.
I have a unlocked iPhone from the States that has a pay as you go O2 SIM card in it. Not the phone I got with the SIM clearly LOL. My husband has a unlocked iPhone from the States as well, but has a SIM with a 02 calling plan. Can work either way.
Can I use my pre pay SIM in ANY phone as long as it's unlocked? Not sure how SIMs work.
Ya sure you can use any prepaid GSM sim in any GSM unlocked phone freely else if the phone is locked to some other network provider then it wont accept your prepaid sim until you unlock it ...If your mobile belongs to blackberry then you cna easily unlock it using sites like UnBBLock.com here they are rendering network unlock code for all blackberry mobile models at reliable cost .Else if you want to unlock some other mobile model then visit sites like Unlock-Zone.com here they are rendering network unlock code for all mobile models at reliable cost .After unlocking the phone you can freely use it with any GSM sim ...