T-Mobile UK
 

After looking rates, etc. over I decided to buy a new T-Mobile UK SIM on ebay for our upcoming trip to Great Britain. My understanding is this comes with no credit on the SIM. Is there anyway to top it off online and register it prior to arrival in the UK? Also, anyone out there know what you do to add international calling to the USA so you get the best rate on this card?

Try and register it on their website online. You will need to the SIM in the phone and be able to receive a SMS. I think this works abroad too. Go to: http://www.t-mobile.co.uk/service/your-account/signup/

For calls to USA there is nothing you need to do. You can call USA for only 3p/min via an 07755 access number. T-Mobiles own rates are not as good as that.
Check out: http://www.yourcallworld.com/Country...px?country=USA

Thanks! That is great advice. Now If I can find a good deal like that with my Telenor SIM for Norway I will be very happy!!

BTW, you don't want to put money on your TMO SIM until you reach the UK -- that's because they give you a number of things free for a few days upon the first topup (free internet for 10 days, several free international SMS, several free picture messages).

If you send a text with INT to the number 441, it enables 5p/min calling to several Central/East European countries (and costs nothing to do this), if you think you might be calling there. Use YourCallWorld for other cheap international calls.