I would like to get some feedback from everyone on the use of out calling applications in ministry. How popular are they? What applications are being used? What are people's experiences with them?

My church recently purchased Phonetree to send out voice notifications and it got me thinking. By day I develop voice applications using the open source PBX Asterisk. As I was working, I realized that it would not be hard for me to develop a open source out calling application based on Asterisk. With trixbox.org making a complete Asterisk install very easy, I think an application like this could be very usable in ministry.