I always go online. Makes it more fun and easier if you ask me. I only call if I really can't find anything I want, but I usually get the same information as I found online.
Calling or checking online will have the same results in terms of what is available. Personally I think there is an advantage to checking online. I think you have a quicker chance of snapping up something that opens up. Calling in seems to take forever to me. Not that I mind listening to the music...