There are actually several services to which you can subscribe in North America, available using forms of Viaccess, Irdeto and several other lesser known encryption formats. These encryption types do not marry to the receiver, so the card can be used with any embedded receiver or receiver with CI and a cam that supports the encryption format.
Globecast uses Nagravision, and the card is married to the receiver. Nagravision encryption is available by subscription if the content provider is supplied the receiver's unique identification keys. This is the reason that a Globcast subscription card can only be used in receivers approved for use with their system.