Hi i need some advice from people that know, rather than a sale person who hasn't a clue

. I have been given a 8700g which was on 02 but has now been unlocked. I am at the moment using a 8120 Pearl on Orange, so my question is can i just swap my sim from the 8120 and add it to the 8700 and still receive my email's etc? If not what are the implications?
cheers
Ridz