Can I remove a SIM card & put it into another iPhone?

I have two iPhones, & I would like to know if I could remove the SIM card from one of my iPhones & insert it into the other one?
If I do, what will happen?

Post this question again in the correct category.

Consumer Electronics >> Cell/Mobile Phones & Plans.

You're more 'likely' to get some answers there!

It would work only if the carriers between them are the same. If not the other iPhone would have to be unlocked.