When receiving the invite, a small phone icon will appear at the bottom left of the Radar, indicating that the player has unread join invites.
These job invites will be offered for the player to host if they are offered by their contact, or alternatively be offered as a job to join if offered by another player. While in GTA Online Freemode, the player will occasionally receive job invites from their Contacts, such as Martin Madrazo and Lester Crest.
The Job Invites option in the in-game phone on the PS3 version.