We don't currently have an SMS system in OwnerRez, although that's something we have plans to do.
One thing you could do would be to use Zapier and Twilio to transform OR triggered emails into SMS's to the guest.
Zapier is an integration tool that takes info from one app and passes it to another.
#1 - So if you set up an email integration in Zapier: https://parser.zapier.com/, and then configure OR with a trigger that sends an email on check-in and departure to that Zapier email address including the guest phone number, Zapier would be able to pick up the info.
#2 - Then set up Twilio which allows you to send SMS: https://zapier.com/apps/twilio/integrations with Zapier -- a Twilio account is a buck a month for the phone number + $0.0075 per message, so very affordable. And connect the incoming email trigger into Zapier in step 1 to send the SMS to the guest using Twilio.
It's a bit roundabout to go through that method, but it should work and get the SMS to the guest in a timely manner.
