Upvote:1
1) Yes your phone can work overseas. With Sprint it seems that you will have to request for them to unlock the phone for international use. They appear to have a requirement that you are an existing customer in good standing - which I take to mean that you pay your bills. Call Sprint Worldwide Care on 888.226.7212 to get it done.
2) Plenty of the uk operators do Pay as you go plans, or monthly plans depending on what you're after in a plan.
e.g. O2 Pay and go
20 pounds - 250 mins, 2500 texts and 500MB data (doubles after 3 months)
15 pounds - 300 minutes, 3000 texts, All-you-can-eat data
etc. Shop around for what you are after. Sims for these companies should be free (or cheap - 99c) according to UK friends.
There is aslo t-mobile, giffgaff and others.
3) Viber is an awesome app. Though there is a UK phone co called Lebara who appear to have US calling included in their 29 pound plan. So that could be an option.