The online play itself should be free, but charge for the advanced online features xbox is known for. A free user should be able to hop online and have fun, but if they want the full "live experience" they pay a premium. Knowing microsoft they'd take this too far and probably prevent free users from using headsets.
Demon's Souls Official Thread | Currently playing: Left 4 Dead 2, LittleBigPlanet 2, Magicka