I'm attending grad school abroad and am hoping to use my mini with a different sim card so I don't have to buy a new phone. Is this possible?
If you are going overseas, get a new phone and provider there. You MIGHT be able to use it on a very limited basis using a foreign carrier's SIM.
It was recommended to buy a phone in the US because they are more expensive in the UK.
The UK uses different bands and frequencies than the US. It's not about the cost of the phone...it's how much the service will cost you. Compare plan costs, not phone costs.