Prepaid mobile phones that work on both the British Isles and mainland Europe.

Any prepaid mobile phone bought in the UK or anywhere else in the EU will work in most other European countries. You can get them from larger supermarkets (Tesco, Sainsbury's) and many "high street" shops. Cost £20, if not cheaper. Before buying:

• Check which countries it works in (usually most of Europe).
• Check you know the cost of using it in another country. This is the so-called "Roaming Rate" and should be no more than 50% above the domestic rate.
• Check you know how to top it up via the internet. You will not find a branch of the shop you bought it from in a different country.
• If you buy it in the UK, the charger will have a British plug, you will need an adapter for other European countries (and vice-versa if you buy it in mainland Europe).
• If you buy it in the UK, it will have a UK phone number.

Finally, check out these 2 sites. They are both companies offering phones with cheap international rates:
www.lebara.com
www.lycamobile.co.uk

Thomas, if you have a compatible (unlocked) phone such as an iPhone 4s, 5, 5s you may be better off just buying a sim card. I just returned from Scotland and England. I paid 10 pounds for an O2 card from Tesco. It gave me 100 minutes of talk time and 500mb of data. I was surprised to find upon my return that it roams with the AT&T mobile network here in the States. I must caution you that if you go to Scotland and some areas of England phone reception and most certainly internet is spotty to non-existant on a mobile device.
Hope this helps.

I used a 3 UK card (GBP15 for 30 days) that includes many minutes of calls and more importantly for me All-you-can-eat data when I was in UK previously.

I could even use data in Italy and Austria but not Germany. They have a long list of "Feel At Home" Euro countries that enable you to use data when in those countries. Please look up 3 UK website for details.

Hope this helps.

Thanks for the input everyone! I'm in Europe 2-3 times per year for 1-2 months at a time and just want a cheap prepaid phone I can throw in my bag, not worry about, and "reactivate" or "top-up" as necessary each time I return to Europe (I would prefer a network that would allow me to keep the assigned EU number even if I don't use the phone for months at a time). Do the major prepaid brands sold at your typical grocery store/Tesco, etc. all share the same networks? I take it the real issue is then the roaming charges between countries. I haven't paid a roaming fee in the U.S. in over a decade and no longer want to pay for the ridiculous AT&T international rates.

Try the Carphone Warehouse. They sell cheap unlocked PAYG phones and will advise on the best call plan for your needs. Not all their cheap models are shown on the site and the shop stock changes frequently. They buy up old (relative term) models from the manufacturers. Several outlets in Belfast.

http://www.carphonewarehouse.com/mobiles/pay-as-you-go