Difference between VVX300 and VVX301

Hi,

I have gone through the Polycom site several times and read the datasheet for the VVX300 line.  I can't seem to find what the difference is between the VVX300 and VVX301.  Same goes for VVX310 and VVX311.

Can anybody provide some clarification or even a link to a document that explains the differences?

Thanks,

Ricardo