Very nice job! Last month I also adapted a rotary phone but I replaced the insides with a Bluetooth chip (and some more). Now I can use it as a headset for my smartphone or laptop. While you had to learn about SIP and voltage converters I had to learn about Bluetooth and digital audio protocols. Looks like we both had fun ;)
https://blog.waleson.com/2024/10/bakelite-to-future-1950s-ro...