Others have noted problems using RemoteRig with U-verse and suggested a hardware solution, however I have found it possible to connect with tweaks to the SIP address and residential gateway firewall.
I use U-verse for internet, TV and telephone (therefore their VOiP). I initially had trouble connecting to my remote TS-480 and attributed that to the residential gateway's firewall blocking SIP. I tried to set up the RemoteRig Control with DMZ Plus, but for unclear reasons the gateway simply gave me an error message. So, my solution was to change the address for SIP from 5060 to 5080 on both remote and control units, and then create three pinholes in the firewall for 5080, 11000 and 12000. Now it seems to be working fine for me.
SIP Out port 5080
SIP In port 5080
Audio Out port 11000
Audio In port 11000
Command Out port 12000
Command In port 12000
External SIP In port 5080
External Audio In port 11000
External Cmd In port 12000
73, Craig AE7I