I've reviewed a lot of threads, and still can't quite decide which way to go with sim cards, callback systems and calling cards.

I too will be traveling in a couple of weeks, to London and then to Ibiza in Spain. I purchased a tri-band international cell, and have been trying to decide on which sim card to buy. We will also be making 2 other trips this year, one back to Spain (Bilboa) and then one in China. We need to be fairly accessible for contact back to the USA for business. However, it's not necessarily that important to maintain one phone number. I think I understand the incoming call deal, that fairly universally is free to me, and I have a really cheap internet phone that will be either .03USD or .14USD from the phone in USA.

I've read the threads about a united-mobile sim card and using callbackworld. I of course want the best of all worlds for the cheapest pricing and most convenience. My questions are:
If I use callbackworld, can I only receive callbacks to one number?
Is it cheapest to get a sim card in each country rather than the international roaming one?
I read there is a way to use calling card with a mobile to "trick the system" and get a cheaper rate. Is this possible?

I'll stop here to get started.

i believe that you will go zero responses on how to "beat the system".

Well it's not beat the system.....callbackworld will give you when you sign up 3 callback trigger numbers which you can peg to whatever mobile numbers you want and you can change them on the fly via the web so that's not a problem....

I would get a prepaid sim for the UK (take a look at mobile world) and a prepaid sim for Spain (I think they're relatively cheap but I'm not all that familiar with Spanish sims...read up about them on www.prepaidgsm.net).

I know nothing about a Chinese prepaid sim however China is listed by United Mobile as one of the countries where you get the free incoming calls so callbackworld will work...whether this will mean you're best off using united mobile for the other two, just United Mobile for China and prepaid sims for the other two or prepaid sims in China too will mean you're going to have to do a bit of research on www.prepaidgsm.net where there are people who actually are pretty smart when it comes to prepaid sims...not the people here who throw out so much wrong and idiotic information.

Now if I had to vote, like I say, I would check out the prepaid situation in China, you can always fall back on United Mobile there and get prepaid sims in the UK (very cheap) and Span (I think they're cheap there)...

Hope that helps.

Thanks for the input. I think the callbackworld concept sounds great, and just getting sims for each country is the easiest.

After several years of buying a sim in each country I went to, I got a United Mobile Sim and just used it on a trip to Portugal, Denmark and Sweden in July and it worked great. I would have had to buy three seperate Sim cards without it so I'm pretty sure it saved me money. And as long as I remember to use it once in the next nine months to keep it active (which I can do here at home in the US) then it should be available for future trips. I go to Europe about twice a year and usually to different countries so it sounded like a good deal to me. So far (one trip) it's worked fine.