Woah woah, 300 people? I've been using GroupMe for a few groups of friends, but no group is bigger than 8 people. I think a reply-all text based chat with even 30 people would be too big. It sucks that there was a bug that let you create a group of 300 but I don't think that is what they intended to be.
So recently I heard about Groupme.com at the TechCrunch Disrupt conference. It is a mobile application that you can get for free (only good thing). It allows you to add people into a "group". After selecting who you would like to be in your group, it sends the same mobile phone number to everyone you have selected. By texting this number selected for your "group" you can then text message to each other and see whateverone says...example it will show up as Danielle … more