I have Polycom vvx310 phones. Under a previous FreePBX installation (6.12.65-30) I had two of the phones working, extensions 100 and 101. I then wiped out my previous installation because I was just experimenting at this point and didn't need to be up and running just yet. I am now running FreePBX 13 (10.13.66, Asterisk 13).
When I added in the two extensions, using the same phones with the new secrets, I could not get them to register with the PBX server. The extensions are setup as SIP (not PJSIP). The add new extension screen says that SIP uses port 5061. I had previously used 5060 and so ignored the 5061 and went with 5060 and the phones could not register. I then switched to 5061 with the same results. Note that although the add extnesion screen said SIP uses 5060, the advanced tab screen for extension 100 had the port set to 5060. I was guessing maybe registration is done through one port and the rest of it is through another port.
Polycomm's web phone setup has SIP Server setup and SIP Outbound Proxy setup. These both take port numbers and it isn't clear to me if they should be the same port. There is also a SIP Line Identification in which the secret is used.
In order to get clear debugging information I set all ports to 5060 and used a secret to match my line number (100).
The following is the CLI output when the phone tries to register (or authorize) with the PBX server.
Connected to Asterisk 13.5.0 currently running on localhost (pid = 8928)
[2015-11-16 15:09:34] WARNING[9055]: chan_sip.c:16653 check_auth: username mismatch, have <100>, digest has <>
[2015-11-16 15:09:34] NOTICE[9055]: chan_sip.c:27498 handle_request_subscribe: Failed to authenticate device "Thorpy Gumflap" ;tag=C6D9D4EF-6D3BE76E for SUBSCRIBE
[2015-11-16 15:09:35] WARNING[9055]: chan_sip.c:16653 check_auth: username mismatch, have <100>, digest has <>
[2015-11-16 15:09:35] NOTICE[9055]: chan_sip.c:27875 handle_request_register: Registration from '' failed for '192.168.1.5:5060' - Username/auth name mismatch
[2015-11-16 15:09:41] WARNING[9055]: chan_sip.c:16653 check_auth: username mismatch, have <100>, digest has <>
[2015-11-16 15:09:41] NOTICE[9055]: chan_sip.c:27498 handle_request_subscribe: Failed to authenticate device "Thorpy Gumflap" ;tag=C16B15F4-378E46C3 for SUBSCRIBE
localhost*CLI>
Note that NAT is set to enable because that is how I had it setup previously, but from what I understand, it is not necessary because all my phones are on the same LAN behind the firewall.
Cheers!