The UNIX phylosophy is that every program should do one thing but do it the best way. And all your problems could be solved combining several programs. I don't know lots of OpenBSD, but under linux there is s/w mgetty. It comes with utility callback. Therefore that I suggest is take mgetty for answering calls. write your program to ask for phone number and check for presence in your list of allowed numbers. If you find - exec() callback. Otherwise - just exit().