An alternative to the phone tree is the phone circle. There, the initiator calls person one, who calls person two, who calls person three, until the last person is called. The last person then calls the initiator, who then knows that the circle has been completed, and everyone has been called. Phone circles are best for groups of a dozen or less people. If the initiator hasn't received his confirmation call on time, he can begin calling through the circle, to see where the circle was broken.
Phone trees are much more effective than phone circles at reaching larger groups of people rapidly.
Their weakness is that if one person near the top of the tree neglects to make his calls, a large number of people down the line will never be notified. Thus, the phone tree organizers need to make spot calls, to check the progress of the message down the tree. Telephone trees are used for rapid mobilization, when there's no time to wait until the next club meeting. Trees can tell members about upcoming legislative hearings, or remind them to vote on election day, or urge them to attend a rally. The tree message has to be simple, because complicated messages get garbled when passed through several people.