David,
Is the hotline a VOIP service? Can you upload an audio file to it, or do you have to call it and leave a recording?
If you have to call and leave a recording you could use a variation of this:
to call, jump through the prompts, and then read the tweet out, which gets recorded.
If you can upload an audio file then I would have one of the many processes watching for a Tweet grab it, convert it to an audio file and then upload it to the phone.
I’d check with Twilio, I bet they would love to have someone build that process and document it as “another cool Twilio thing” on their site.
Hope some of those help 
Cheers,
Dave