Here are some pointers to know more about it, besides Minimodem
Softwares for RX/TX:
FLDigi - http://www.w1hkj.com/
MMTTY - https://hamsoft.ca/
(2016 - Radio Discussion on FLDigi vs MTTTY - https://community.flexradio.com/flexradio/topics/fldigi-vs-mmtty )
Presentation on using RPI with Amazon Echo -
Look at http://kitt.ai/ as mentioned in the presentation if you're into smart homes and privacy.
Exploring Amazon Echo, part 1 - Intercepting Firmware Updates - https://medium.com/@micaksica/exploring-the-amazon-echo-dot-part-1-intercepting-firmware-updates-c7e0f9408b59
Exploring Amazon Echo, part 2 - Into MediaTek utility hell - https://medium.com/@micaksica/exploring-the-amazon-echo-dot-part-2-into-mediatek-utility-hell-b452f62e5e87
Good YT vids:
Hope this helps and puts us on the right train of thought!