Typo wrote You have to go to the T on the map to talk to trevor. once you do that all of merrywether lester and lamar will call you eventually and tell you you can call them for things like helicopter pickups and muggers

Yea I was level 90 and couldn't use half of the stuff I went to Trevor on the map and within 20 minutes everything unlocked automatically

You have to do some missions to unlock him