Can you put an payg sim (o2) into a iphone 4?

Can you put an payg sim (o2) into a iphone 4?

Yes you can, but it will only work if the iPhone is locked to O2 or unlocked.

If the phone was originally bought locked to Orange for instance, then the O2 PAYG SIM card won't work.

But you won't damage the phone at all by trying. Just make sure it is the right size SIM card (any other won't fit).