I work for a company that uses VoIP through a switch a couple hundred miles south of here. The voice quality is at times quite poor. Packets are dropped and it sounds like the connection is cutting out and it's sometimes very hard to understand the calling party. What's up?
There are a variety of problems that could be at work here. The first place to look is at the physical layer. Have the circuits tested and have your physical infrastructure tested to be sure that the problems do not lie in the cabling infrastructure (this is actually very common). Walls get moved, etc. and can cause problems there. Once that layer is tested and fixed or certified, the other thing to do is look at your traffic reports and packets sent.
There will be some latency with the switch being 200 miles away, but as long as your traffic is moving the way it should, the voice traffic should still be audible. If you have a frame relay circuit, for instance, that is undersized but with the ability to burst to a higher speed, it is possible that you don't have enough bandwidth to handle both your voice and data traffic. Pay particular attention to any discards or errors in your routers and switches. You may be asking too much from your network.
It is a good idea to trend your traffic and compare highest traffic levels to the times of day when your calls are dropping. For instance, if you lose calls at 8 in the morning when everyone if firing up their PC's and checking email, traffic may be a culprit. Check with your carrier to determine what reports that they have that can assist you. It may also be a combination of both. If cabling and circuits are in disrepair, they can cause increased traffic that is not going to help.