The service will be called Passport. It will be available as a trial and will be completely free. Vodafone customers will be able to travel to pretty much any country that Vodafone operates in and use minutes and texts from their regular call plans. Pay-as-you-go customers will get their usual domestic rate. Sadly, data roaming charges will still apply, but will be capped per megabyte as per new EU regulations.
This is pretty incredible news and will hopefully force a few of the other big mobile phone companies into doing the same thing (do it now O2, do it right now).
With any luck data roaming will be the next thing to become a worldwide standard rate and will simply be built into call plans.