Can I use a UK Virgin phone in the US with a US SIM card?
You'd need to get the phone unlocked so it can use any sim card, but I'm sure by doing that you would break the Terms and Conditions of the contract you have.
Yes you can, depending on your phone you may need to have it unlocked. You can unlock your phone by purchasing an unlock code, customer service can sort this out for you.
The phone should work fine in the USA as most phones are compatible.
hope this helps