Would love to see an SMS option! I don't keep fb messenger installed on my phone.
Is there another chat platform you'd prefer to use? Slack? Google Hangouts? Telegram?
Maybe another SMS service offers that? If so, I'd certainly consider SMS again.
One option would be to re-enable the SMS option for people who deposit money to cover the SMS fees. Mark them up 100% (so 2c per SMS or something) and you'll have a built-in profit margin.