I was curious what the limit was on the number of people you can add to an iMessages group. Assuming everyone was on iMessages (i.e. everyone shows up as blue).
I read nothing about a limit in the different user guides for iOS devices (e.g. iPhone User Guide [PDF, 17MB]). Because of that I think there is no limit for groups.
I believe 9 members is the maximum amount that can participate in a single iMessage group thread.
I don't know the reason for this arbitrary number but people in my company have discovered this on their own. We are organized into groups of 12 and have not been able to include the entire group without a third-party app.
With regards to other comments made earlier in this string, there are countless reasons businesses would use group texting in fairly large groups. For example, sales teams, management team, or dept. teams can use messaging for rapid means of communication.
Messaging is quickly becoming the preferred means of communication where I work when rapid responses from groups are required or when everyone is spread out geographically. Email tends to be slower even if it is pushed to users devices. We primarily use email for longer messages and less urgent matters.