No. You can only have one active headset connected to a base unit at anytime. However you can use the active headset connected with the base, and have an inactive headset charging on that same base at the same time. You must note that when the inactive headset is placed on the base for charging, the active headset in use will be temporarily disconnected from its paired base unit. You will need to push the Call Control button on the headset so that it will reconnect with the base.
Also, you can charge a second battery for the remote in the base of the CA/CS10 product while one is being used but not for the CS50, CS55, Voyager 510s or Supra Plus Wireless. You can purchase a separate charger for the other models and have a second headset available.
Once the second headset is charged and placed on the original base a resubscription/pairing process must be done for the base to recognize the new headset.
For the CS50 & CS55 the separate charger is model SSP2358-01. this product is built to order and can be purchased from any distributor. CS50/CS55 Resubscription Instructions
For the Supra Plus Wireless unit the charger is yet to be released. Supra Plus Wireless Pairing Instructions
The Voyager 510S comes with a separate charger for charging the headset individually. Voyager 510s Pairing Instructions