This will depend on your phone and NOT the headset. To answer without the need to put the handset off-hook, your phone typically needs to have the following:
1. Headset jack
2. Handsfree or Headset button
3. Off-Hook Dialing feature
If your phone does not have any of the above you will need to lift the handset and put it off-hook to answer the phone AND use the headset.
Note: If you do not have any of the above but still wish to use a headset without picking up the receiver with every call you can purchase a wireless headset.
A wireless that is purchased with a "remote lifter" simplifies your calling experience. See video below for details on using the wireless headset and remote lifter.