Welcome to SwitchPi website! We are concentrate on bringing the Raspberry Pi to Asterisk VoIP communication world.
We are producing few modules, such as PiTDM, PiGSM, OAK and DAWN modules.
The OAK provides a module which can support one onboard FXO port and one FXO or FXS port with modularization, for more details, check it out in Oak specifications.
The PiTDM provides a module which can support up to 4 FXS or FXO modules.
We would like you to update the PiTDM firmware to the new version which based on Raspbx or Digium official GUI, that will let you play PiTDM module by much more easily. You can get it by following this manual for Raspbx and this manual for Digium official GUI, also, we just released a new SwitchPi GUI, which is a much more reliable GUI.
The PiGSM provides a module which can support a quad-band GSM/GPRS, that is integrated a SIM800L module, that works on frequencies GSM850MHz, EGSM900MHz, DCS1800MHz and PCS1900MHz. That features GPRS multi-slot class 12/ class 10 (optional) and supports the GPRS coding schemes CS-1, CS-2, CS-3, and CS-4.