They merged, but are still seperate. Each company has like 5 exclusive channels, but for like 2 dollars a month you can get the opposite companies channles as well.
Example, sirius has howard stern, xm has opie and anthony.
I have xm only for o&a, and is easily the best spent money for entertainment to me since I am on the road 2 or so hours a day usually.
Also can confirm the worst customer service company in the world.