Now that we have the 4Q06 numbers, we can take a look at gross subscriber additions. The reason why gross subscribers are important is shows the exact market penetration of each company and how well they're attracting new subscribers.

So in Q4 2006, XM added 1,064,887 gross subscribers (when compared to 1,373,876 in Q4 2005). For the full year in 2006, XM added 3,866,481 gross subscribers (compared to 4,130,437 in full-year 2005).

Above is a graph that illustrates the quarterly gross subscriber additions from the beginning of 2005 through the EOY 2006.

It's obvious that XM's momentum has slowed, even when you remove churn (people who have dropped the service) and just look gross subscriber additions, it's clear that XM's subscriber growth rate is softening.

The big hit comes from the retail side of things, where 4Q06 retail subs were 540,474 versus 935,707 in 4Q05, while OEM gross subscribers are actually up for the fourth quarter (524,413 vs 438,169).