If you own the phone outright, it won't be locked to a particular provider. So, yes. You may need a new sim card but your provider should just be able to send you the relevant sized one.
That's not true, you can buy a phone outright that's still locked to a network. You have to get the (i forget the name) code off the provider for the handset in question to be able to release it.
If you own the phone outright, it won't be locked to a particular provider. So, yes. You may need a new sim card but your provider should just be able to send you the relevant sized one.