Are you referring to XM Nav Traffic? If so, that's out. For aftermarket it's a plugin to a GPS system. Like Garmin you can get the GXM-30. Crazy expensive though. $200 for the receiver with no service. $60/yr with a FULL PRICE paid XM subscription, or $120 without.
For the money, the Total Traffic one covers more, the receiver is $120, includes 15 months of service, and is $60/yr thereafter.