I'm pleased that you had some success with this project. I didn't experience the SPI issue which you referred to but I did experience similar problems with internal functions in a timer call back chain not being forced to remain in ram. That was solved at the latest by core 2.4.0. Anyway, someone may well benefit from your troubleshooting.
I'm now adding the latest production version of this application v1_12 which has the following features:
- A Message Waiting Indicator
- An Accept Spam Call on screen button, allowing the user to accept a spam call during the period the ringing is suppressed.
The PHP code, database format, documentation (apart from the supplement below) etc. remain the same as in the original version published earlier in the thread.
Also included are some examples of the format of message waiting notifications (MDMF). However, you can also use the following tool to visualize the various Caller Id and message formats and even generate the audio signals: Telephone Caller ID AFSK Generator - Exhibition / Gallery - Arduino Forum
I'm currently documenting a simpler system aimed more at beginners who can take the basic core consisting of the demodulator and parser, and incrementally add their own functionality to it without having to touch the core logic. It is ATmega328P based. Hopefully, it will appear soon.
ESP_Telephone_Callerid_v1_12_published.zip (39.5 KB)
MDMF Message Waiting Data Format.pdf (341 KB)