What's the difference?

Standard tank helmet (without headset):

Intended only for mechanical head protection (soft pads made of horsehair or foam cushioned impacts against the hard elements of the tank's turret and hull).

It had protective ear pockets or flaps, but no electronics (phones or wires) inside.

Helmet intercom (with headset):

A complete means of communication and protection.

Special fabric or rubber earpieces (earphones) were sewn into the ear pockets, and laryngophones were attached to the throat (for speech transmission without interference from the roaring tank engine). A wire with a plug ran from these to connect to the tank intercom (TPU) or radio.

Who owned them?

Helmet phones with a headset:

These belonged to crew members who vitally needed constant communication: the tank commander, gunner, loader (depending on the crew's roster and the availability of a radio), and, without fail, the driver (for communication with the commander).

Regular helmets (or helmet phones without a headset attached or removed):

These were issued to crew members who had less need for radio communication inside the vehicle, or during radio shortages in the early years of the Great Patriotic War, when only command vehicles were equipped with radios (others communicated with flags or gestures). Later, with the widespread adoption of radio communications, helmet phones became the standard for all personnel in armored forces.