(covers information from several alternate timelines)
Photonic torpedoes were equipped with a variable yield antimatter warhead. They could be launched while a ship was traveling at warp speed as well as when it was traveling at sublight speeds. They had over fifty times greater range than the previous spatial torpedoes. The variable yield was described by Malcolm Reed as being able to "knock the com array off a shuttlepod without scratching the hull, or put a three-kilometer crater into an asteroid." Antimatter to the warheads on NX-class starships was provided by the ships antimatter reserves. (ENT: "The Expanse", "Hatchery")
A warning label on the torpedo casings classified the photonic torpedo as an antimatter ordnance device that must be maintained on power at all times. It also included warnings that the photonic torpedo employed magnetic isolation fields, that if breached would release lethal levels of energetic gamma rays. The duty tactical officer was to be notified before loading or offloading the antimatter used by the torpedo. Magnetic devices were not to be operated near the torpedo, as they could interfere with the containment field. (Star Trek: Enterprise)
Starfleet began to utilize the technology in 2153, when it began installation of the torpedoes aboard Enterprise NX-01 following its return to Earth. These new weapons were installed in the ship's armory to better prepare the craft for searching for the Xindi weapon. (ENT: "The Expanse")
The use of antimatter warheads aboard Earth starships came as quite a surprise to attacking Klingons. In 2153, they sustained enough damage that they were forced to discontinue their pursuit of Enterprise on course to the Delphic Expanse. However, this form of torpedo still could not effectively penetrate the deflector shielding of a typical Klingon Bird-of-Prey when most shield power was transferred to the section under attack. (ENT: "The Expanse")
Klingon torpedo technology of the time, nevertheless, appeared to be much more advanced than both Earth and Vulcan technology, as some of their ships were already equipped with photon torpedoes. (ENT: "Sleeping Dogs")
In the mirror universe, photonic torpedoes were already in use on the Emmette-type starships. The weapons were used during an assault on the Lunar colonies, that occurred some time before the introduction of the NX-class of starships in 2151. (ENT: "In a Mirror, Darkly", "In a Mirror, Darkly, Part II")
It became something of a Starfleet tradition to place dead crewmembers inside an empty torpedo casing, and often such torpedoes were launched into space. For such a burial in space by the crew, the Captain of the starship often conducted the funeral service.
In the final draft script of "The Expanse", photonic torpedoes were described thus; "The torpedoes are similar to those seen in previous Star Trek series, but more primitive in design."
According to StarTrek.com, photonic torpedoes were the earliest model of a Starfleet photon torpedo. According to the site, photonic torpedoes were also armed with a matter/antimatter charge and an optional timer. They had simpler internal systems than the spatial torpedoes. For storage, the torpedoes were powered down to a safe mode to protect them from a failure of the magnetic field around the antimatter charge. 
VOY: "Living Witness" also supports the idea that photonic and photon torpedoes are synonymous. In the episode, a 31st century Kyrian calls a 24th century Starfleet photon torpedo a photonic torpedo. It is also possible the Kyrians were simply mistaken about the name. These accounts, though, suggest the term "photon torpedo" might be a shortening of the original term, similar to the way "cellular telephone" has been shortened over time to "cell phone".
In any case, by 2233, Starfleet was using photon torpedoes, as seen in the film Star Trek when the USS Kelvin was defending itself, and as they were identified in the script of the film.  According to the Star Trek: The Next Generation Technical Manual, Starfleet began work on the photon torpedo in 2215. ENT: "Sleeping Dogs" established that the Klingon Empire was using photon torpedoes as early as 2151.
A photonic torpedo casing was auctioned off in the It's A Wrap! sale and auction.