I asked this on the Euro blog where Gavin Russel is in the hotseat. His reply :
That reads exactly like Warhawk. If three people join a game, team balancing will put one onto the opposition team. This would mean no B3D posse ruling the FP world. We'd end up fighting each other. The only slivver of hope that there are better options is the developers have suggested a developer versus blog-reader fight, which would mean some selection of teammates. But twice now they have said about players switching teams being the only option to team up with the people you want to team up with.@Shifty_Geezer,
No game can have more than 16 players per team. You may choose to set up a 32 game exclusively for friends – players can then select the team they wish to be on, based on the number of available (balanced) slots.
As for joining a friends game, once in the player can opt to change team as long as there’s space to do so.