(/c)all [number]
Allows you to call another player (/call displays the list of all important governmental numbers, such as Medic, LCPD, etc.).
/call h [housenumber]
Allows you to call the house phone of another player.
/sms [number] [text]
Command to send a SMS message to another player.
(/p)ickup
Command to pick up an incoming call.
(/h)angup
Allows you to hang up and end a conversation.
/turn_on/off
Allows you to turn your cellphone on or off.
/loudspeaker
Command to turn your cellphone's loudspeaker on, so all players nearby can listen into the conversation between you and the other player you're having a conversation with (/loudspeaker to disable).