Cryptic Studios announced earlier this year that it would be turning Star Trek Online into a free-to-play MMO at some point in 2011, but that timetable has now been pushed back into 2012. January 17, 2012. That's the day Trek goes F2P, Cryptic now confirms.
You can get the details on how the new pricing structure will work on Cryptic's website, but I'll explain it here. The no-cost Silver membership gives you full access to the game but limited community and support features. Gold membership costs $15 per month and includes things like in-game chat as well as extra character slots and inventory space, veteran rewards and priority login on the game's servers.
Source: Star Trek Online website