Is there a limit on the amount of phone numbers allowed in a Group MMS?

I have tried searching online and could not find the answer to my issue, and have had no luck. I have an iPhone 5 with iOS 6.1.3 software which says on my phone that it is up to date.I recently have been using Group MMS to send out the same text to multiple people at once. It's great and all, but it will only allow me to add a total of 10 phone numbers to one group. If I try to type in an 11th person, that phone number disappears when I begin to type the text message. I've been messing with it today and talked to another iPhone users and was told they have not had this problem with sending to more than ten phone numbers themselves. I was wondering if there is a setting in the phone I need to change, is there some limit to the phone numbers allowed in a single Group MMS, is it a problem with the phone itself, etc.?

Thanks!