TL;DR - I've written a short, simple Python script to run on my Raspberry Pi, which will make a Twilio voice call to my Ericsson whenever* something noteworthy happens (e.g. I receive an email).
*in practice, this could be expensive as Twilio charges 2p/min for outgoing calls - it'll realistically be more cost-effective to run the Python script a few times a day, if there's anything new to share.
Long and possibly boring explanation: I originally planned to make this project work 'the other way round' i.e. I wanted to be able to dial my Twilio phone number from the Ericsson, causing a script to be run on my Raspberry Pi, which would read RSS feeds/Twitter posts/emails to me down the phone line (i.e. I make outgoing calls to Twilio from the phone).
However, there are a few issues with this approach:
a) security - I would basically have to make whatever I wanted to share available publicly on the internet (I'm not publishing my emails for the whole world to see!)
b) cost - Twilio charges 2.9p/min for incoming calls, as opposed to 2p/min for outgoing calls (approximately, as of April 2022)
c) inconvenience - I have to keep ringing my Twilio number even though there might be no new information to share.
d) clumsiness - it was a right pain to set up an Apache/Flask/No-IP combo to serve my content over the internet, and I'm convinced it only worked by sheer good luck! :-)
So, instead, I've decided that my Ericsson should receive incoming calls from Twilio - a bit like receiving a notification on your smartphone.