Look at the Nortel / Avaya 2033, a UNIISTIM IP conference phone for the CS1000, CS2000, and BCM series. They are designed by Polycom, but Nortel provided the UNISTIM portions of the firmware to make it communicate with the Nortel solutions. They have great sound quality. I currently have about 50 of them deployed, distributed in most of our conference rooms across the globe.
The only issue I've seem with them is the display gets a little funky after a several months of use, but a reboot will clear that. (It's due to a firmware glitch. A firmware upgrade should correct our problem, but our service provider will not support the upgrade.)
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