The Plantronics Savi W740 has officially been discontinued (2019) from Plantronics (now Poly) and replaced by the Savi 8240. Overall, the two headsets are almost identical but there were some improvements from the Savi W740 to the Savi 8240.
#1 Improved ear hooks
The Plantronics Savi 8240 now has improved ear hooks that has a mix of rubber and flexible plastic, for improved comfort.
#2 Better placement of volume/mute controls
This is a nice improvement because on the Savi W740, most people didn't know there was a mute button. On the Plantronics Savi 8240, it's clearly labeled where the volume controls as well as the mute/unmute.
#3 More durability
The Savi 8240 looks to be thicker and more reinforced for a stronger design.