If you are only making light use of your phone, the standard roaming rates for calling the UK or numbers within the country you are visiting, or even for using small quantities of data, are very modest (see the links provided by kids and bandofbrothers), and will probably be more cost-effective than the £3 charged on days when you use your phone under EuroTraveller. Last year I was in Greece and then Germany for about a week on each occasion, and just using standard roaming charges, it was only costing me about 50p a day for the occasional call, and enough data to check emails.
