the only legit way is for you to subscribe directly from the provider. no legal provider will provide you their services via cardsharing method.
there are several ways, actually, but the most popular would be to connect via internet and get the card details from the server. others are selling the hardware and will provide you the card details off another satellite transmission.
how long will this last? nobody can tell if you are buying from a dealer whose intentions are just to sell enough receivers then cut off the card sharing device (this happened to the blackbox, and will soon happen to the twin tuner receivers they are selling which gets the card sharing via satellite transponder).
you are free to do card sharing though. just make sure you share or get your card details off a friend who has the legit card (somebody you can trust). search for the spider network thread on this forum and you should be on your way on card sharing.