Chiming in here - same results as everyone else, for the most part. On US-Mobile (T-Mobile), initially had to downgrade Messages to get it to connect, updated, and it worked great for 24 hours (including send/receive in group messages with iPhones).
I just re-downgraded one of the phones and it connected within 15 seconds and all is well again. I'm going to let that one bake to see if it breaks. Since it sounds like the team knows what's up with T-Mobile, I'm assuming we're in a holding pattern until that's resolved.
Appreciate everyone's feedback and help on this, and am sending a donation to the Graphene team shortly.