Each simultaneous call costs you ~100Kbps. An SMS is 140 bytes, and limited by desired SMS throughput. I use a T-Mobile femtocell with a SpaceX Dishy, but VSAT (64 Kbps up to 8 Mbps) should be fine for SMS only.
McMurdo could run their own BTS and provide SMS access only to mobile phones if the desire and funding was available. This would give you a legit mobile network registration.
