Telecom Awesome

• dc-unlocker

Radio

• librecellular

PSTN

DTMF

• A HTML 5 AudioContex DTMF Tone Generation Tool
• Recreating phone sounds with Web Audio
• wikipedia Precise tone plan
  • dial tone - 350, 440 Hz at −13 dBm
  • ringing tone - 440, 480 Hz at −19 dBm, 2s ON and 4s OFF
  • low tone - busy tone - 480, 620 Hz at −24 dBm, half second ON and one half second OFF
    • reorder tone - 0.25 second ON and 0.25 second OFF
  • high tone - 480 Hz at –17 dBm
• https://www.npmjs.com/search?q=dtmf

GSM

• https://shufflingbytes.com/posts/hacking-goip-gsm-gateway/