A Sim is associated with a users account. So either 'pay monthly', and then you'll need to have a credit check, set up an account, and then get sent a Sim, or 'pay as you go', in which case you can probably just buy one for a tenner in most phone shops, and slap it in any phone you choose, and after a couple of Sim updates, the phone will be a PAYG.
Why a RAZR, particularly, anyway? Sounds like this will be your first phone, and the RAZR gets mixed reviews (as well as Motorola kit not generally being very reliable). Maybe a better choice for a first time user would be a Nokia? I've had a few, and they all still work just fine, and Nokia come top in most reliability surveys.