This project uses Raspberry PI B2 that act mainly as PBX with image of http://raspberry-asterisk.org/, but in it I change some stuffs on door-berry project software and now it works as one device door-berry + pbx + gsm dongle based on chan_dongle. I use 16GB class 4 card. The interesting thing are:
1. The power source for the PI - I use Meanwell PSC-60A module and AMSR2-7805-NZ stabilizer. The PI is shutdown safely when the backup battery is around below 10V.
2. With great thanks to Nick Gammon I add an arduino nano that communicates with the PI on serial with logical level convertor and also communicate to other arduinos through RS485 module and the Nick's protocol. It acts like a mediator, because I am not sure how python will act through USB-RS485 communicator. All this give unlimited automation for homes and small buildings open/close doors with a phone call or with a web interface, read sensor data and many other