I managed to get outbound calls working fairly easily by setting up my VOIP account and adding phones in webadmin.
Inbound was a problem as I was getting a "no authority found" error. The only way I discovered to fix it was to abandon the realtime mysql-based iax.conf config and switch instead to a flat-file. Also it was more than a matter of simply porting the lines from the database to the flat file as the mysql configuration was simply wrong. There is no automatically generated
[##########]
type=user
context=from-trunk-##########
section in the database (where ########## is my phone number) which apparently is required.
In summary, everything seems to be working now after doing:
1. comment out the line "iax.conf => mysql,general,ast_config" in /etc/asterisk/extconfig.conf
2. move everything from the mysql table for iax.conf to an actual iax.conf file in /etc/asterisk
3. add the code section above to the iax.conf file
4. reload asterisk
Obviously this is a band-aid solution, but it has things going for the time being.