We will be doing a walking tour in the UK for about 10 days, and will need to call ahead to our hosts to confirm arrival on several days during the journey. Our itinerary does not allow for us to stop at a mobile phone shop in the UK (arriving Manchester airport, taking train to Lake district same day) - so we need to order something online. I have found some options on amazon.co.uk for inexpensive mobile phones with "pay as you go" plans. How does that work? Can we have our calls billed to a US credit card? How do we set it up?