I specifically asked TomTom Support that question, and they said I don't have to do anything, it will just work. This is in fact how my Garmin worked, so their claim seemed reasonable.
And yes, the tuning defauls to automatic.
When I was using a Garmin, I had to do a lot of fiddling with the antenna position, and it still didn't work that well (in the NY area), though a replacement receiver they sent me seemed to work better than the original.
Baesd on my experience with my Garmin, ClearChannel's maps grossly overstate their coverage. I have yet to get a signal with the antenna and GPS unit in my van. On the driveway, holding the GPS up in the air, with the TMC receiver dangling below, yes, but not in the van.
Given the known problems in my area, I may be taking TomTom Traffic for a spin to see how it does.