I received a text message from this number it says:  thanks for calling Plantronics Vocalyst! To activate your free one year service go to www.plantronics.com/vocalyst.  I went directly to the Plantronics website and set a message to customer service asking if this came from them.

Just received the same message purportedly from Plantronics. I never called them, although I do have a Plantronics bluetooth device.