BioWare and Electronic Arts held off admirably, but implementing a free-to-play model in Star Wars: The Old Republic seemed inevitable to keep the player base from falling off. If you're looking to swoop in without paying a subscription fee, take a look at this chart -- it details the restrictions you will face, of which there are many.
Yes, you will still be able to get your class up to level 50 -- and that's pretty good, I might add -- but Flashpoints, Warzones, and Space Missions are limited on a weekly basis. Other things, such as a longer quick-travel cooldown and restrictions on inventories and cargo holds seem like they could add to make for a less-than-ideal player experience.
Of course, that's the intent, as they've got to make money somehow. At the same time, there's nothing to say BioWare can't tweak these restrictions going forward.