TruVoice Professional U10 Single Ear ProfessionalU10

Q: Does this work with Cisco 3905 series phone?

It plugs into the back of our CISCO IP phones as long as the headset terminates in a standard phone jack

Q: Does this headset work with the callany ht500?

You will need the headset with the U10P to work with the Callany HT500. See below for the correct version :) https://www.amazon.com/dp/B0748L42BL?ref=myi_title_dp Thanks

Q: Will this work with a Cisco CP-8811 phone?

It should work with any Cisco phone as it comes with the adapter that has a regular phone connection on the end. Also according to the description it says all 6000, 7800, and 8000 series, which would include 8811