I managed to get a TCP server running on an UNO with a Sim808 module that was apparently accepting incoming http requests.
I tried the standard port 80, and then a port >1024 to test, but apparently Ting is NAT'ing all of their ip addresses and you can't get incoming traffic on them. The address spit back with a AT+CIFSR was a 21.x.x.x address, while a different sketch that hits ipecho.net/plain always spits back a 171.x.x.x address, so I'm pretty confident that it is in fact doing NAT/masquerading.
Any way around this? Is there a different carrier, or port range that would work? I'm thinking I could open a TCP connection from my device to regular server and have the server forward requests back through that, but I'd rather just have the arduino answer them directly.
Anyone had any luck with this?