On Android devices, Zello asynchronous messaging lets you send voice messages to users, even if network connection has been lost by either you or the end user. This can be useful for users who lose connection for a brief period of time while driving under a tunnel or riding in an elevator.

1. An arrow followed by a number shows queued messages, which are received by the user when they are back online.

2. Open the history to see the status of the messages. The hollow arrow with a line underneath means Zello is sending the message.  

3. A hollow arrow indicates the message has been sent. 

4. The arrow turns solid when the user has received the message. 

This feature will be coming to iPhone users soon!