I have a customer who had an Asterisk system that died and my salesman sold them a SV8100 to run his Polycom phones on. The customer has two models of phone. The Soundpoint IP550 and the Soundpoint IP330.
The 550 I have had very little trouble getting connected. The 330 I have programmed exactly the same as the 550 but it will not connect to the NEC.
Any ideas?

First thing to check is whether you have enough 3rd party SIP licenses on the system.

We have 25. Plenty

Simple things first can you browse into that phone and see it on the network? Also are you at the latest firmware? You also have to make sure that extension is in the numbering plan as a SIP endpoint.

you should have unregistered port on the system and used them for SIP extension and i think the polycom phones run in the authentication mode