M12 Vista: Can I use both the headset and the handset simultaneously?
(without switching between the two)?
No, you cannot use both the handset and the headset simultaneously, but you can switch between the two.
For example: If you are on the handset and wish to switch to the headset, all you need to do is lay the handset down on the table (do not hang it up) and hit the headset button on the amplifier. Or, if you are already on the headset and want to switch to the handset, pick up the handset and hit the headset button on the amplifier to turn the headset off.
More details are available in your User's Guide.