Hands-Free turns your Mac into a Bluetooth headset. When you dial or answer a call in BluePhoneElite, it will route the audio from your cell phone to your computer's microphone and speakers. Hands-Free will work with any phone that implements the Bluetooth Hands-Free Profile. Consult your phone's documentation for this information.
For most phones, the answer is no. Unexpected problems may occur if you attempt to connect a Bluetooth headset and BluePhoneElite's Hands-Free to your phone at the same time. The phone may decide to accept both connections, drop the existing connection, reject the new connection, or just freak out in general.
It is not currently possible to use a Bluetooth headset (paired with your Mac) as the Hands-Free audio device; OS X only supports a single Bluetooth audio connection at a time.
To prevent Hands-Free from routing a call's audio to your computer, use the Suspend Hands-Free option from the device's menu icon or above the services list in the Bluetooth Phones tab of the preferences. Most phones will still be able to dial calls and display caller ID, but the phone will use its own microphone and speakers instead of your computer's.
Some phones only support Hands-Free. Hands-Free can not be suspended on these phones.