has anyone adapted Meeting Scheduler to also work via sms?

what exactly do you have in mind? 👀

Being able to text someone to find available times and then ask them for an email address to send them the cal invite for a mutually convenient time.

sure! bit of an advanced build but you could take the meeting notetaker, add twilio actions to send SMS and ask for the email, use the calendar actions to find available times you can send to the person too, very doable 🙂