I only wanted to point this out (not to encourage this at all because its probably breaking the TOS of Bioware) BUT it is VERY much possible to play two characters on the same account at the same time.
I was playing a trooper and was on skype with a buddy. He wanted to try swtor out so I gave him my info and stuff expecting to be d'ced off as he logged on. Well I wasnt! In fact, he made a sith inquisitor on a different realm and even showed me. I said ok this is garbage...your faking. Show me MY toon while I play a different one. So he then logged off and onto my trooper...showed me on Skype him playing MY trooper while I was playing a Jedi gaurdian on the same server and account. LOL
wtf is this Bioware!?