i think u r a bit confused of the definition of erlang. of course, as u mentioned an erlang s the volume of traffic carried in one hour. Even though it very well means that if a subscriber uses the traffic for continuous one hour he gives us 1 erlang, it doesnt mean that all the subscriber uses call for one hour.
u cannot mingle no. of channels with erlang. Coz there s no concept of giving a single channel to a subscriber. There are hopping principles etc etc. An ocean called channel concepts. Where as Erlang is jus a unit. Jus to denote that how many erlangs or how much money he has given us.
Hope u r clear.