Travel to Spain and France
 

Can anyone please recommend the best card with free incoming, with usage of callbackworld or similar? I'd like the most economical card.

Thank you

All sim-cards in Europe have free incoming calls, so that's really not a problem. I never used callbackworld, do they have a special number to call or is it just a local landline number for each country? I fear most sim-cards could not work or work at high prices.

For "real" callback they have US DID numbers which don't answer (calling them triggers the callback). So, if your phone number is allowed to make calls to USA (int'l calls not barred and credit isn't too low) you can trigger a callback.
They also offer some calltrough numbers (800 or 00800) in some countries. When you use them, CBW service is functionally equivalent to a postpaid calling card. And, of course rates for usage of those number are usually higher than for callback calls.

BTW, in July '06 I asked you to check the two CBW access numbers for Italy and it turned out that they don't work ;).