Odo appears on the bridge of the Defiant using a holocommunicator

The holographic communicator (holo-communicator or holocom for short) was a communication system which allowed two or more parties to send holographic images to each other, simulating face-to-face interaction.

The technology was first used by Starfleet in 2373, installed on the bridges of ships including the USS Defiant and USS Malinche. (DS9 episode: "For the Uniform")

A holo-communicator was also installed in Captain Benjamin Sisko's office on Deep Space 9, and at Starfleet Command on Earth. (DS9 episode: "Doctor Bashir, I Presume")

Also in 2373, Captain Sisko contacted Kira Nerys from the Defiant using the holocommunicator. (DS9 short story: "Where I Fell Before My Enemy")

During the Dominion War, increased security measures at the Palais de la Concorde led to the decision by the Palais de la Concorde Press Liaison to eliminate in-person press conferences, and instead use holocom technology to allow journalists to attend remotely. This arrangement proved popular enough to continue even after the war. (ST novel: Articles of the Federation)

Starfleet continued to use holographic communication for larger meetings, such as a briefing held during the Gateways Crisis in 2376 and another following the Borg Invasion of 2381. (ST - Gateways novels: Doors Into Chaos, Demons of Air and Darkness, Cold Wars, TNG novel: Losing the Peace)

Other races have employed similar technology, including Kurros of the Think Tank (VOY episode: "Think Tank") and Shinzon of Remus. (TNG movie: Star Trek Nemesis)

In 2382, Ronarek used a holographic, temporal communicator to communicate with Jamran Harnoth, his sponsor. (DTI novel: Watching the Clock)