Nextiva

Below is an example of a working authenticated SIP trunk from Nextiva.

SIP Provider: Nextiva
User Type: friend
DTMF Mode: rfc2833
RFC2833 Compensate: no
Disabled: No
Host: bt.voipdnsservers.com
Port Default
Register: Custom (fill in appropriate values:  register => authname:password@bt.voipdnsservers.com/authname
Authentication: Yes
Auth User: Default
From User: Default
From Domain: Custom - bt.voipdnsservers.com
Realm: Default
Outbound Proxy: Disabled
Outbound Proxy Port: Default
Username: authname
Secret: password
Inbound CallerID: blank
Outbound CallerID Name: Company Name
Outbound Caller ID Number: authname  (nextiva controls callerID, and requries authname here)
Call Limit: fill in whatever the nextiva trunk plan allows
Qualify: 30000

All other settings can be left as default or as-desired with the case of allowing call recording.