This excerpt taken from the SIRI 10-K filed Mar 10, 2009.
Traffic News Services
A number of providers also compete with the XM and SIRIUS traffic services. Clear Channel and Tele Atlas deliver nationwide traffic information for the top 50 markets to in-vehicle navigation systems using RDS/TMC, the radio broadcast standard technology for delivering traffic and travel information to drivers. There are also services that provide real-time traffic information to Internet-enabled cell phones or other hand held devices, but these are available only in limited markets and the associated data plan costs in addition to normal cell phone rates may make the offering undesirable to many users.