Speakerphones are a get-what-you-pay-for kind of thing. Polycom speakerphones are expensive, but they work really well.
Being entrenched in the corporate culture, if you tried to sell my department on a brand new "speakerphone" that required the use of my cell phone, or was enhanced by my cell phone, I'm going to ask why my phone isn't corporate issued then, if I have to use it on all of my work conference calls.
If everyone used their own phone, then you might as well dial into a bridge, and I think that's a solved problem.
I love Polycoms and was sad to see my employeer recently replace them with Cisco units (who designed the button layout of the 7937?).