It is possible to do a call "hand-off" from one device (i.e. laptop) to another (i.e. mobile) running Dialpad app ?

Indeed you can. We call it "Call Flip" and you can move from mobile to desktop to tablet to deskphone without ever dropping the call or losing any of the features regardless of endpoint. Just go to the device you want the call to move to and hit "Switch Call to this Device" and it will pull the call into that device without anybody noticing. More info here: https://www.dialpad.com/features/call-flip/