My 3810 was successfully configured after a switch was made to SIP protocol instead of H.323. It seems that many are moving to SIP protocol because of more “robust signalling performance”.
Also the codec is not specified in the configuration in order to allow the default codec (G.729r8) to operate. It appears that explicitly stating the codec causes a problem.
I am still not certain what caused the problem with the Carrier Access but the connection through it is now okay.
Answer supervision is still a problem and from a price point view the Pleaides with it voice detection capability is the better choice out there. This also can be solved by utilizing a billing service or NOC that can provide answer detection. Especially with its ability to be controlled remotely.