Some more information to this card:
It has two IMSI numbers to be switched.
IMSI #1 is from a US carrier and it works on AT&T and T-Mobile in the US. This IMSI does not work outside the US.
IMSI #2 is the +44 carrier from jersey telecom.
So you have to switch to IMSI #1 when you are in the US.
Both numbers can be reached all the time anyway.
The tariff says in Zone 1 + 2 incoming calls are free with +44, 19ct/min with +1 - 19ct setup fee occur all the time.
Henning is testing this card for some time already now and he said it works stable. his full post in german here:
Der United-Mobile Thread - Telefon-Treff
Chris