Looking at tadiran's Sip terminal interoperability table it doesn't show that polycom as being a support sip device, unfortunately tadiran's sip is rather restricted on the terminal end. If your interested I have been able to setup an Asterisk pbx as a network node using sip trunks to a tadiran, and then you can add your polycom's as extensions on the asterisk with network numbers on the tadiran. email if your interested.