While members can be manually added to a group by a group administrator (perfect if you are, for example, establishing a customer loyalty group and want to upload your existing database), a key advantage of GrpTXT is that individuals can join or leave a group simply by sending a text message.  Once an individual sends the necessary text to join a group, their details are automatically captured and they will be added as a member of the group (and will receive all texts sent to the group) until such time as they chose to remove themselves, or a group administrator manually removes them from the group.