Virgin is a virtual operator using the Orange network, and is cheap for most things (data being an exception). Worth checking out if Orange is good in the areas you'll be in. The only real way to know that, though, is to ask people with experience of the areas you'll be in.

I've always found the service in
The Phone House to be good, and they publish a catalogue making it easy to compare tariffs. Agreed, though, that it's better to buy in France in any case.