Originally Posted by Mr Chaotix
I had only just done the Fame or Shame mission before attempting the Three Man Army achievement. So at that point Franklin and Trevor hadn't met.
What I did was, I called up Trevor first and asked him to hang out, then called Franklin. Went over and picked up Franklin first then Trevor.
This is when I tried it, right after this mission but it wouldn't let me call Trevor to hangout. I'll try again in a minute, because all of them are just hanging around the city.
Right now I'm at the point of Franklin being able to meet Lester, which makes me believe he will then meet everyone else. I'll try now before this and then try again after if all have met each other.
Edit: Ok, it can be done as soon as the 'Fame or Shame' mission is complete but I'd wait a bit or do another mission to be sure. Didn't work for me then, but has now and I've done about 2 missions since then.
So yeah. There you go. Add it in!!!!!!!!!