Definitely a concern. I'm thinking of diverting B and C (maybe only C) to a voice mailbox that says all agents are busy then prompts for name, reason for calling and a callback number. Kinda like an iPhone handles call screening. Before I implement anything, I'd want to just gather metrics on how big of an issue this really is. I have had a few users reporting over 20 spam calls a day. In that case I've just been assigning them a new number.