Apologies for offending AT&T. True, I don't know of any system phones with top-quality speakerphone included.
I am a bit surprised that there aren't a lot of inexpensive competitors to Polycom by now. The electronics are easy with DSP now, and the other components are reasonably inexpensive.
Anyone remember AT&T's "tower" speakerphone? It had a microphone 3 feet tall, standing over a 6 inch cube. Holes in the microphone pole, at roughly 3 inch intervals, collected sound in a way to minimize room echo. Circa 1985.