I am not sure what the GSM DC connector is but OTS makes Buddy Phone for this mask that plugs into one of the side P-Ports
Golem Gear, Inc. - Buddy Phone for FFM
Very compact solution - just a P-port with "push to talk" button and an Earpiece.
Easy to use, just spit out the bitepiece (you want to have it on any CCR with this FFM) and talk, then catch the bitepiece back.
Kybrt, I dive the mask with contacts, but there is enough room there for small "Lennon" glasses, the seal might be good enough that it will not leak even with wire sides going to your ears. Have not tried that though.