OK guys, I'm usually not a person to do this, but...please actually read what the OP wrote, perhaps? We know it's possible to do a mass messaging on the phone, but the OP wanted to know if it's possible to do it without having to type in names of the contacts each and every time.
As far as I know, it's not built into any version of i(Phone)OS. I just tried typing the name of a group from my address book into the recipient field, and it didn't work, no matter how I toggled messaging settings.
It seems weird to me that it isn't built into the OS, as it would be really useful. My students check their text messages much more than they check e-mail, so this would be a really useful thing to be able to do without having to deal with an app...but if an app is the only way, I think it's worth investigating, for me anyway.