[PhotoJim]

Andy has it. Mobile carriers generate revenue from inbound calls in most countries, because the rates to call them are significantly higher than to call standard lines.

My guess is that this SIM will have free inbound calls only if the call comes from the +447 number as a result. The fee the carrier generates from the inbound call might have enough margin to permit routing the call to the US, plus paying the airtime to the roaming carrier.

I can't see that happening if the call is received on the +1 number.

Still, a lot of European people have sufficiently inexpensive rates to call +447 mobiles. And US travelers can ensure that if people want to bother them while on their American vacation, the caller can foot the bill. It doesn't seem too unfair.