SMS Event Announcements .. ability to send to Non-Responders just like email announcements
Integrate SMS notifications into Event Communications using similar categories as Email, including Announcements, Reminders and Confirmation SMS.
Most importantly, we need ability to send SMS Event Announcement to members that have a status of "No Reply" for an event (filter out those that are Registered or Not Attending). In the current SMS implementation, all members will receive a text message regardless if they have responded or not. This may feel like spam to some as they have already registered with the system that they are "Attending" or "Not Attending"

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LeaPash commented
I ran into the same issue and ended up using https://sms.to to reach both members and non-members for event reminders. It was pretty easy to plug in my list, and it didn’t require everyone to be part of my database. The delivery rate was solid, and I liked being able to track who clicked the links. Definitely made communication feel smoother and faster for last-minute updates.