The Plantronics Discovery 645 is a slight improvement over the Plantronics Discovery 640. It maintains all the same features and design of its predecessor, along with the multiple charging options. The only difference is that the 645 includes a digital signal-processing chip that reduces background noise and improves audio quality. However, the 645 has since been superseded by the Plantronics Discovery 655. The 655 also has multiple charging options, though it has omitted the different adapters for cell phone chargers. Please read our review of the Discovery 655 for more details.