March 2, 2022 
A friend had figured out how to get the dial url working in FileMaker (a sample of this is also in the demo file) and was wondering how sending an SMS file might work. There are a number of ways to do send SMS messages from a FileMaker database, including using an API service such as Twillo or Claris Connect. What I was looking for though, was a free and non-server based option, something that could be done from a standalone database on a Mac computer or an iPhone in the field. This method could also work in a networked setup, it is send only, any responses are not going to show up in FileMaker magically.
I found two sources for using the url method in FileMaker online. One blog post from Hi Voltage in Australia had a demo file that had the basics in place, but it didn’t generate a text message. Your iPhone permissions need to be configured properly (see the Hi Voltage article for more detailed setup instructions). Then I found someone had improved on their script with some lines of code on a FileMaker Today Forum post.
I don’t see a method in the url scheme to have the message actually send automatically, it will require the user to click the send button.
I have tested this on both Mac and iOS, not Windows. It might work there, I am not sure how friendly Windows computers are with iPhones to setup the tel:// protocol and send sms urls. If anyone tests this please let me know in the comments.
It is really a very simple script. The script assumes you have two fields, a phone number field and a text to send field. The text to send field is optional and if it is empty, the message is simply started when you get to Apple Messages.
You will have to setup your own controls to make sure it is a mobile number, because obviously SMS messages don’t work when sent to landlines.
This script takes two fields, so if you copy this script into your own database, please update line 5 and 6 in the script with your own fields.
Hope this is useful.
See also
Part 2: Sending SMS Messages from FileMaker using Apple Shortcuts
Part 3: Sending SMS from FileMaker with AppleScript
Dialing for Dollars – Getting FileMaker to Call or Text to an iPhone, Skype, Facetime or Zoom
HomeBase Software 
Doug, As always, THANK YOU! Thank you not only for researching your ideas, but for simplifying them so beautifully! You have always been so good about sharing what works, what doesn’t, ways that others might be able to improve them, and being open to both criticism and suggestions. Please know that if/when we ever get to gather at DevCon/Engage in the future, you should NEVER have to buy your own drinks. As a community we owe you a huge debt of gratitude!
Thanks Jim. That is nice to hear.