It seems that the most daunting and complex part of an IP Telephony network is the nuts and bolts of Quality of Service and the configuration of gateways, dial-peers, route plans and the like. But it only seems this way until you start dealing with users who have had their expectations for service options and flexibility set extraordinarily high.
One area that has potential for problems is the endpoint. Aside from all the flavors of IP phones, by which we usually mean Ethernet-attached phones, there are many types of soft-phones, applications, and analog-to-IP phone converters available on the market today, and users will want them all. While your design should accommodate all of these, you may want to restrict many of these at the outset if you can.
The reason for this is simply support. Just as your organization has a single standard make and model of PC for users' desktop computing, you might want to start your IP telephony rollout gradually, by putting only a single make/model of IP Phone in your environment. Over time, add additional devices as necessary to satisfy user requirements.
The danger of adding many types devices all at once is mass confusion. First, the optimal settings for each device take time to determine. Ensuring compatibility between devices takes even more time. But even if you've got a crack networking team, remember that users can adopt only so much technology at a time. Consider that few users are even aware of half of the features on their current phones, much less proficient in their use. And when users don't know how to do something, human nature is always to blame the tools (and the network, of course). By supplying your users a light, but steady stream of new toys and education, you'll have much better results.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.