You should look at the create_amp_*.pl perl scripts in /usr/pluto/bin... These are the scripts that set up things for the various VOIP providers with our underlying asterisk. These can be used in the Web Admin under "Wizard > Devices > Phone Lines"
As for adding it to the Setup Wizard...This screen is currently hard-coded in HA Designer, and probably will not change before the planned Orbiter rewrite.
-Thom