The rise of VoIP and other applications means that few network administrators today are afforded the luxury of grooming their networks to cope with the bursty traffic they were trained to deliver.
What we are dealing with now has a name and that name is converged networks. Small businesses often have the luxury of removing the "converged" part of the problem by installing a second broadband link, just to handle VoIP traffic. This probably doesn't guarantee them high quality real-time connections for every voice call but it does stop the existing data from getting bogged down in the battle for bandwidth. Essentially, it pushes the problem upstream and makes it an ISP issue, which will probably evolve into a bum-biter down the track as ISPs start charging extra for VoIP traffic.
For those with networks too large to simply duplicate for the sake of separating VoIP traffic, the router and switch vendors have begun adding features to their products to aid in the process of keeping the data pipes flowing smoothly. Of course that means you'll probably have to spring a fistful of dollars for some new kit, but that's why we have IT budgets, and don't forget to allow some wiggle-room for training. Although there are point-and-click setup interfaces on most network kit these days, you'll find it more than useful to get your network techs up to speed with the new protocols being used for VoIP such as Session Initiation Protocol (SIP).
SIP is a signalling protocol developed by the Internet Engineering Task Force (IETF) for initiating, managing and terminating voice and video sessions across packet networks. Borrowing from ubiquitous Internet protocols, the flexibility of SIP enables it to accommodate features and services such as call control services, mobility and interoperability with hybrid and IP PBXs. More importantly, this protocol helps you to future-proof your networks. Vendors such as Alcatel, Avaya, Cisco and Microsoft have already incorporated SIP into their products.