Buying an American Verizon iPhone 4S to use in the UK?

Is this possible, I'm planning on buying an American Verizon iPhone 4S to use in the UK, from eBay! Will I get charged by Verizon for roaming or can I just install a new SIM from T-Mobile for exmaple?

No, you'll need to buy an unlocked iPhone 4S if you want to use it in the UK. The Verizon iPhone doesn't use a sim card meaning you can only use it with Verizon and not with T-Mobile.