Are the CS500 and new Savi Headsets and Bases interchangeable?

YES!

The corresponding CS500 and Savi model number headsets will work on either base:

I.E. The CS540 headset will work on the Savi W740 base.

The CS530 headset will work on the Savi W730 base.

Since the Bluetooth connectivity of the Savi series is in the base, the Customer will still have that functionality when pairing a CS500 headset to the Savi base.