(Probably even worse than Chris's)

I'm off to a festival tomorrow, and don't want to take my new Desire because even I don't lose it or damage it, the battery will run out by Friday night.

Q: Can I just put the SIM card into my old Motorola Razr and it'll all be cool? Obviously my new phone has millions of clever gizmos and dohickeys that I'm worried might be messed up if I remove the SIM.