A GPS function where you could select a location and a marker on your map would appear with a line (if possible) of that location, including important locations like LSCH, LSPD, SFDS, ammunation and hospitals build in as basic)
move /getphone or what the command currently is to a phone item, you can select if you want to be in the phones database yourself and it'd be automatically in there.
A tracer function (addon to hacking) which could replace /area, leave /area for admins. Tracer function could trace people (by phone number maybe, make it more realistic than /area id) and people can also disable/ dispose their phones.
Spy-on (addon to hacking) spy on what the people near you are talking/ texting about.
Newspaper, replace it with /ad, add a newspaper link/ app to the phone, you'd be able to see all ads of the past 24/ 48 hours on there (increase the price of /ad too and allow one per person per 12 hours?)
Gambling app, allow players to gamble with eachother using their bank account and phone
Just some basic ideas I had in mind, will add more shortly.