Buy a 3 sim card on arrival - I think they cost GBP 1.-, top up with GBP 10.- (I think that's the minimum topup), and you're good to go. 1p/mb, 2p/sms, 3p/min calling. The value doesn't expire so it's useful for any future trips there too (unless you actually use up the full GB of data...)
// Edit: not sure if that will work in a Verizon phone, I'm not very familiar with what US networks do to phones. It should work in most phones that take a normal sim card though.