For Bluetooth headsets, it is recommended to read the user guide carefully, which is provided with the Bluetooth device in order to configure the device with the IP phones. Connect the base stations to the correct jack of the IP phones and also connect the headset to the base station.
Refer to Plantronics for more information about the Bluetooth devices.
It is possible to connect an external microphone to the headset port, but an external jack must be used. Cisco does not have such products, but there are likely some third party vendors that sell these.
The Cisco IP phone 7940/7960 supports a four- or six-wire headset jack. A Plantronics H series compatible is required.
Pair 1, which is the middle pair, pins 2 and 3, and Pair 2, which is the outside pair, pins 1 and 4, must be kept together, end to end. The phase reversal is not critical if the supplied handset is used, but can trigger hum if another piece of equipment is used, such as a recorder, headset, or amplifier.