So one of the things you can do with Asterisk and Freeswitch on the PSTN network is hook up a Cisco/Linksys SPA122 adapter or use something more recent. If usin

So one of the things you can do with Asterisk and Freeswitch on the PSTN network is hook up a Cisco/Linksys SPA122 adapter or use something more recent. If using a VOIP line, some providers in some countries let you control the VOIP line entirely so you can spoof phone numbers to the PSTN network, and as Asterisk/Freeswitch lets you do things like call record and will send the ringing tones (or what ever you choose to play to someone calling your VOIP line) before you answer it, you can also listen to people talking waiting for you to pick up and answer or direct to a voicebox. In effect you can create a voicebox where you never get charged for leaving a message, ideally for covert activities, legal or otherwise, and its done because of the way the channels are handled. Whilst you are playing the dialling tone back to the caller, you have asterisk/freeswitch setup to record the call from the time the tones are played to the caller, only you never answer and the caller can leave whatever message on the PBX because officially according to internation standards a call was never made and thus charged for. I dont know the legality of it, but it seems to be an exploitable weakness in international standards, for covert activity. There's lots of things you can do with these and Freeswitch also works on a Pi2B. You'll find some telco providers have just taken Asterisk or Freeswitch and recoded it enough to class it as their own, but you could run an entire phone company in a country on Asterisk/Freeswitch if the HW is powerful enough. If you look at the Caller ID standards, the EU standard is based on the old dialup v.23 baud rate. https://en.wikipedia.org/wiki/Caller_ID#Operation https://en.wikipedia.org/wiki/Caller_ID#Operation https://en.wikipedia.org/wiki/ITU_V.23 https://en.wikipedia.org/wiki/ITU_V.23 So if you want to do some HW hacking, you could start with any old modem and turn it into your own SPA122, and once you have done that you could look at taking an ADSL router and turn it into a SPA122 of sorts. These are just devices with some hw capabilities but could do more.