This will basically just work. The TA908e isn't involved. Multicast is independent of the IP addressing of the TA908e (which is unicast). You may need to configure the switches for IGMP if there is more than one switch involved but in most cases it just works. Note that the Polycom multicast paging feature is limited to phones on the same physical LAN.
Just enabling the feature on the Polycoms didn't seem to work. I then enabled the following on the Adtran, and it does seem to work now:
interface eth 0/1
ip mcast-stub fixed
ip igmp static-group 18.104.22.168
Why did this make it work?
Do you think there is anything on the Netgear switch I would need to configure to make it work without this command applied on the Adtran?
I'm not sure how this configuration could have helped get this application working. The stub and static-group configuration options are generally setup to allow multicast to traverse two different routed interfaces. You may need to make sure the switch is forwarding everything, but otherwise this might be an issue that we need to troubleshoot over the phone by calling 888-423-8726 to create an ADTRAN Technical Support ticket. We would likely need to compare packet captures before and after applying these settings to understand the traffic pattern differences.