I'm looking for a telephony provider which will ring number A on an incoming call, and if number A does not answer within x seconds, ring number B, then number C if B does not answer within x seconds. Don't want to install hardware on our premises, and a flat monthly rate is preferred for the service without having to worry about running over the specified number of minutes (as phone.com bills in tiers, and my agency prefers a flat rate).
Your kind assistance would be appreciated.