Hi, my name is Yair, I've been a Zoho developer for the past 2 years, implementing solutions and process inside Zoho for a small telecom company where the client gave me all the responsibility of migrating from the old CRM to Zoho. I implemented first the CRM, later the workflows and Blueprints process, later that year we start to develop our own functions through deluge, all of that I did it myself. This year we started to implement our own widgets and connection to different systems that we use through the API and widgets. All the system was implemented and develop by me personally.
I implemented a process similar to the one you're proposing but with appointments in a third party app through the events, and they were in sync, something pretty similar to your proposal.
In your particular case I would recommend to explore the widgets pre-install in Zoho, or to develop our own widget to Send custom sms in addition to using the sms feature of activities.
We can do this in 7 days or less, but if the price is to hi for you we can put more time into development and reduce the costs.
I believe we (together) are a right match and the right team for this job, I have done this recently and successfully, I know the API, the functions, and the logic to do it.
Hope we work together in this project
Yair