This is a REALLY interesting SIM for me - as I'm based in the Isle of Man.
I phoned them and discussed it. They're definately Germans, not in Hong Kong.
They say the free incoming ("national") is for the country of the SUBSCRIBER, i.e. if you sign up from Germany, it's Germany, sign up from France, it's France, sign up from the Isle of Man and it's the whole of country code 44. They claim it works in the Isle of Man.
They say the roaming partners are idential to Manx Telecom:
http://www.manxpronto.net/roamingpartners.asp
So it doesn't cover Mexico yet.
Note I'm just reporting what I was told, haven't checked it yet, although I'm ordering one today.
The Isle of Man number system is a little unusual. Fixed phones are +44 1624 followed by six digit numbers starting with 6,7, or 8. Mobiles (on the only network) are +44 7624 followed by six digits numbers starting with 4. So there is a special dialling rule locally, just dial the six digits to get a local fixed or mobile number (e.g. 4xx xxx from a fixed phone is all that's needed to dial a mobile).
So mobile numbers starting with 1 might be a problem. Breaks the local dialling rule (numbers starting with 1 are services, like the operator or 112). Dialling one of their unallocated numbers, with area code, from within the Isle of Man gives the message "this service is not compatible with this call" which might be because the number is not yet in service - or might be to stop anybody using it locally! I'll ask Manx Telecom next.
Note that international incoming calls to GT-sim are charged at the UK mobile rate, as it's with country code 44. BUT note that UK mobiles usually charge more to call the Isle of Man than to call UK mainland mobiles, so if you're a UK user anybody calling you from within the UK might get a suprise on their bill.
[update]
Manx Telecom don't have a rate for calls to these numbers, it's not clear whether they are diallable from the Isle of Man or not, might be barred to block competition. I'm chasing this up with the local company that own that number block (which is not Manx Telecom) before ordering - since the majority of calls I get while travelling are from the Island.
[update 2]
It's been confirmed to me that the number should be diallable locally. And their helpline within that range rings OK. Ordering: note the order form doesn't work with Firefox, and to see the Terms and Conditions click on "privacy policy" (they've used the wrong term). Had another chat with them, there will a better ordering process "soon", and the "only" countries not diallable are satellite phones, and Cuba. The people behind it have been run 26cent.com, which is where the pricing comes from. I've ordered one to play around with, will report back when I've received it.