Will my iphone 4 sim card work in a sony xperia phone?

I just got the iphone 4 on contract (yes stupid I know) but i'm going to buy a sony xperia phone to make up for it, I can't lost my contract though so can I put my iphone 4 sim card (the one on the contract) into a sony xperia prepaid phone?

Only if

the Xperia is unlocked or locked to the same network as the iPhone 4