A grab-bag of low-tech callattendant-related materials.

• Aggressively prepopulate your 'Permitted' list. This can allow you to be more aggressive with filtering, with fewer false positives.

• If you never receive calls from most area codes, consider adding most of them to the Block Numbers regex:

  ^200: B9 - 200 (unused)
  ^201: B9 - 201 (NJ)
  ^202: B9 - 202 (DC)
  ...etc
  

  See callattendant-regex-block-NA-area-codes.txt for a baseline.

• Other regex ideas:

[-\d]{12,}: B9 - 12+ numbers + dashes
[\d]{12,}: B9 - 12+ numbers
^$: BN - empty name
^P$: BN - P(rivate)
^O$: BN - O(ut of area)
^[A-Z][0-9]{14}: BN - spam CID (V)
^\+[\d]: B9 - starts with plus

• List: https://callboot.net/hardware.html
• List: https://ascendis.com/callerid/modems.php

• ffmpeg
• sox (to concatenate multiple WAVs into a single WAV)
• libsox-fmt-mp3
• https://github.com/pndurette/gTTS

• OGG
• ffmpeg -i IC_SIT.ogg -ar 8000 -ac 1 -acodec pcm_u8 IC_SIT.wav

• https://superuser.com/questions/579008/add-1-second-of-silence-to-audio-through-ffmpeg

• ffmpeg -y -f lavfi -i anullsrc=channel_layout=mono:sample_rate=8000 -acodec pcm_u8 -t 1 silence-1s.wav

• ffmpeg -y -f lavfi -i "sine=frequency=825:duration=0.5" -ar 8000 -acodec pcm_u8 beep.wav

• mkdir mp3 wav
• gtts-cli "text here" --output "mp3/filename.mp3"
• ffmpeg -y -i "mp3/filename.mp3" -ar 8000 -ac 1 -acodec pcm_u8 "wav/filename.wav"
• ffmpeg -y -i "mp3/filename.mp3" -ar 8000 -ac 1 -filter:a "atempo=1.2" -acodec pcm_u8 "filename_faster.wav"

• Special Information Tone
• https://robocall.devpost.com/submissions/12817-using-the-special-information-tone-for-disconnected-numbers
• Telcodata.us Area Code + Exchanges lookup