You can now play The Old Republic as much as you please... just don't hit the level cap.
Unfortunately, SW: TOR doesn't seem to be living up to that hype. The MMO peaked at 1.7 million subscribers in February. Since SW: TOR is primarily story-driven, not enough new content was being pumped out to hold subscriber interest, leaving SW:TOR with 400,000 less subscriptions by May.
Perhaps in an attempt to rekindle the fire of subscription numbers, BioWare and EA announced that SW:TOR would be free up to level 15, mimicking the trial period that Blizzard implemented with WoW back in June 2011.
SW: TOR has had free weekends before, where non-subscribers could sign up to get a taste of the game. Now, players can experience SW: TOR whenever they please. The new trial gives them enough time to experience the origin stories of the numerous classes and experience PvP -- just enough of a taste to get a non-subscriber hooked.
The free up to level 15 trial began yesterday. You can participate by signing up and downloading the game client at SW: TOR's free trial page.