In Slide2Talk, the conversation between users goes inside closed / private groups. So you can talk to known persons only.
You can create some group for your family members, another group for your co-workers, one more group for your friends and so on.
The group creator (group admin) specifies the name of the group and some password for the connection. Only users who know the password can join to the group. So group creator should share the password to those users who allowed to join.
Search for groups to join is carried out in the current WiFi network.
Each user specifies his name which is visible to other group users.
Voice messages can be transmitted to all online users of the group simultaneously as well as personally to individual users.