Like the ablative armour, the transphasic torpedoes were given to Voyager's crew by a future version of the ship's own captain. Even though the ship lacked any access to a spacedock or outside support of any kind, it was still a relatively quick procedure to prepare the weapons systems for these devices. At time of writing Starfleet has had little chance to asses the technology, but Voyager used several of them during combat with the Borg when returning to Earth and they were massively effective on this occasion. Voyager was able to destroy a Borg cube with two hits, and a second with only a single hit.1
Starfleet is sure to conduct a rapid assessment of these weapons, and if the Temporal Prime Directive allows then it is highly likely that they will make a fleetwide deployment of them in the near future. It seems certain that this will result in a massive increase in the offensive firepower of all torpedo-equipped vessels. Given that the ablative armour generator technology is also likely to spread through the fleet shortly, it seems that Starfleet will soon eclipse all of its competitors in military strength.