We recently purchased two 7975's and the handsets are different than our 7940's and 7960's. There seems to be a lack of higher pitch. The call volume is good and the clarity is there it just sounds like a more narrow range. I know this sounds petty but I have a few users that would balk at this immediately.
We RMA'd the handsets and I got back one that was the old style and one that was the new.