roman: free cab rides if you don't mind being driven by a guy who isn't shy about making it known that he hates your guts. personally i think it's hilarious and call for rides all the time just to hear what he says

little jacob: call him and he'll appear somewhere close to you with a trunk full of weapons at a discounted price. essentially a cheaper roaming gun shop. well worth the effort

brucie: provides helicopter rides to various areas in the game. no specific spots like burger shot or a gun shop though. mainly intersections. imo not too useful, considering you probably already have roman's perk way before you get this one and you can't take dates with you (in my experience anyway; they never follow you to the top of the building) BUT it's a nice ride, especially at night

carmen/sohohoe: call her and you'll receive a health boost. plus she's a freak and likes the strip club *thumbs up*

kiki/lawchick: call her and you'll lose a few wanted stars. i'm assuming no more than two as she broke up with me almost immediately after i got the perk and i didn't get to use it