IDT Mobile
 

http://cgi.ebay.co.uk/idt-mobile-int...QQcmdZViewItem

Is this a new service? where are they based? what type of number do you get?

I think these are prepaid sims for the UK. They also have for a few other european countries specializing in international calls

There is also a US version called Tuyo that uses the T-Mobile USA network and IDT international long distance:
http://www.tuyo.com/

It launched in the UK in September, an mvno on Orange; they've been in other countries longer.

In the UK, there are also Lebara and Nomi mobile, rumours of Lycatel coming here. And there are also options on all main networks with selected cheap international destinations.



In Ireland, the OP might be interested in using Vodafone's cheap rates to certain countries, sometimes combined with callthrough, to make calls from under 10c per minute

Lebara UK
 

For UK users, I recently got one these PAYG sim for overseas calling, you can also use for roaming in EU 39p/call 19p/receive. Its on vodafone network and call quality is much better than my previous sim from CW mobileworld which used T-Mobile.

http://www.lebara-mobile.co.uk/en/index.php

The website looks interesting. Do you get a normal UK mobile number for incoming calls, and are incoming calls free in the UK like the other mainstream operators?

yes....like the rest of the UK mobile market all incoming direct dialed calls the caller pays not the recipient!

Yes I got a 075 UK number and incoming calls are free. Another new virtual operator offering overseas calls is nomi-mobile...www.nomi-mobile.com, however they do not offer roaming like Lebara. I'm also getting GPRS on Lebara.

Can someone post info on how to use GPRS in Lebara? I've read their entire UK site, but can't find information on how to actually enable GPRS.

I got a Nokia E61, I used the OTA from the Nokia website.

http://www.nokia.co.uk/A4222200

You can also get settings here, see at the bottom of the page

http://www.lebara-mobile.co.uk/en/faq.php