I don't know if this forum developers dabble in telephony related systems development.
Recently know of Asterisk (the Open Source (sort of) Telephony) on developing dialplan and AGI etc.
Then Kannal (the Open Source WAP/SMS Gateway) on developing your SMS application.
Telephony and SMS systems have long been the turf of commercial vendors with strong backing but now with Open Source alternatives, we have a choice.
Welcome anyone who dabble in Asterisk and Kannal to reply.
PS I am learning Asterisk dialpan currently. Will understand Kannal next.