why DoEs voip Cost lEss
A．BECAusE it usEs sEpArAtE sErviCE proviDErs.
B．BECAusE it nEEDs lEss working stuFF to oFFEr sErviCE.
C．BECAusE sErviCE is proviDED through E-mAil.
D．BECAusE sErviCE is ChArgED monthly.