There's a few different iterations of this that pop up from time to time, actually.
The most prominent is of course, the Week 6 Team Match, which you'll be seeing pretty soon. It pits the Godlike Champion and the 3 lower divisions' Runners Up against the Godlike Runner-up and the other 3 Champions. It's only one match a Season though.
The other big one is on the Tournament Boards: Nyarlathotep's Dungeon. It's named after the Lovecraft / Persona2 character. DL members select a group of up to 5 PCs worth 11 points from the list. Characters that are better in team settings, of course, cost more points. Then, the teams run through a series of 'Floors' - each Floor has a chain of 5 team matches against various pre-chosen opponents, and sometimes a Floor has a field effect. Normally, three teams compete at once; each one tackling a different Floor. Victory is determined by votes, and if a team passes a Floor, then they move onto the next 'lower' Floor of the Dungeon. This one appears to be currently on hiatus, unfortunately. It'll probably start up again when Nephrite is less busy, I suppose.
The Strat League is another one that's come up recently. This is a more story-based tournament where whole battalions of PCs face off in a strategic war battle setting, with victory being decided by votes as usual. It needs to be revived because it sounds cool and obviously there's some interest in it *hint hint*.
Also, in general, the Tournament Board will have team-based Tourneys crop up every now and then. If you're willing to explain rules clearly, come up with a roster, and take the time to tally up the results, you're welcome to even post one of your own. I'd suggest looking at some of the pre-existing Tournaments there for reference.
