Take a look at this link. The Tundra is not listed as one of the compatible vehicles yet, but I'm betting it will work. In fact I think I'll give them a call and report back. It's at least better than through Toyota. My dealer tells me that it will be December till they have the Sirius fit kit for the 07 Tundra.
I just talked to tss-radio and they said they would not guarantee it to work. If it is not in the compatible vehicle list you are on your own. They would take it back though, if it doesn't. I was not brave enough, so I went with a cheap plug and play unit for now.