Our Product Team is currently evaluating this feature. In the meantime, you're welcome to cast your vote for it at https://ideas.ringcentral.com/forums/958493-phone-messaging/suggestions/48022952-allow-more-than-10-people-on-a-group-sms.
 

​@khuscherpahl  was checking to see if you are still having the same concern about the 10 sms max per message?

Yes, it is still a concern. Has this feature changed?

As of three months ago, the group text capacity is still limited to 10 people. I might have a solution to help you save time and avoid resending the same message repeatedly.

It's a tool called SendIt, which lets you send multiple texts at once using an import and schedule feature. Take a look at this YouTube tutorial: "Send Multiple Texts at Once with SendIt’s Import Schedule – Tutorial "

Let me know if you have any questions or need help getting started!