You can set up a keyword in FrontlineSMS so that any message beginning with that word triggers the sending number to be added to a particular contact group, or removed from it. This feature can be used to run subscription services, for example, to a particular SMS alert or information service. In this instance you may also want to set an automatic reply, so that people know that they have been successfully subscribed or unsubscribed.

For more information on how to set up and manage keywords, see Keywords in the online Help.
For more information on how to join or leave groups, see Join/Leave Groups in the online Help.