According to the FAQs and our ties to the Bothan Spy Network, you will not be able to earn Cartel Coins in SWTOR.  Some MMOs allow you to earn in game currency by completing quests or deeds (see LOTRO), but it does not appear that this is going to be the case with SWTOR, at least in the beginning.

Cartel coins are giving players an option of purchasing their content “a la carte” instead of paying a mandatory subscription fee just to get into the game.  For me, this is the single most important aspect of the F2P model.  If there is a certain event occurring or a particular quest chain that I would like to check out, with the F2P model, I can log in, feel my way around and then decide if I want to spend any money in order to continue my time.

Many players went back to a F2P game when their SWTOR subscription ran out.  They could go back to another MMO, do the same types of things as they were doing in SWTOR (raiding, PvP, questing) and spend little or no money doing so.

This move to F2P is the right move, and I am sure that it will be a successful one for EA/Bioware.