Seems like I've lost my Blackberry, yay. Expensive mistake...

If I bought the cheapest pay as you go one from a high street store, from random network, would I be able to just pop in my replacement sim and everything's dandy? Or are they locked to networks?

I'm not sure my network does PAYG Blackberries so hence the question.

i just picked up a BB 9300 Curve 3g from the o2 shop and its locked to o2.
Its possible that CPW do generic ones?