Twilio is pretty great but for this use case using Google Voice is a lot simpler (assuming its available in your country)
I recently did this for a firm that is fully remote now during pandemic. They had non voip line for main number. Set the office phone to FW to a GV number and put GV in DND so it goes straight to voicemail which was what they wanted. Then setup GV to send voicemail to email and gmail to forward to slack channel using the basic slack email integration app.
All in all very easy to setup in 20 min or less and get transcribed VM in slack channel with link to play the message as well.
I keep thinking of setting up something like this with Twilio as a backup... I don't trust GV to stay around forever... especially since it seems like they just stopped supporting voicemail transcription for a while (iirc over a month) and the settings and integrations seem to be left to die...
I haven't looked in a while, but running a Virtual PBX via Twilio or similar is really interesting to me... and something I'm surprised more aren't taking on, considering I've seen the amount of what providers for SIP support are charging.
I recently did this for a firm that is fully remote now during pandemic. They had non voip line for main number. Set the office phone to FW to a GV number and put GV in DND so it goes straight to voicemail which was what they wanted. Then setup GV to send voicemail to email and gmail to forward to slack channel using the basic slack email integration app.
All in all very easy to setup in 20 min or less and get transcribed VM in slack channel with link to play the message as well.