I just got a group message that came from a MAXX. It arrived on my Bionic as an SMS.
I grabbed her phone (she sits across from me) and as soon as I type a second recipient into the text app, the word "MMS" appears above the send button. Can't seem to figure out how to toggle it back so SMS, or find a setting that prevents that.
EDIT: I found it. In the messaging settings on her MAXX, there's an option for "Thread Group Conversations" that if checked, will make them send as MMS. I assume the pro of that is that group conversations all appear together? Sorry, not familiar with it, but I know when I send out group texts on my phone, they don't all stay together....when someone responds, their response becomes a separate conversation and there is no "group conversation".
Maybe I need to check my settings in Go SMS (EDIT: I found the option in Go SMS to do this same thing, and will probably leave it on).
Anyways, to the OP, it's probably that setting on the other end causing this.