Q. How do I get a quality VoIP connection?
A. There are a number of ways to get a VoIP connection. You can use your existing internet connection, but this is prone to issues as you are sharing connection with all of your other internet services, email, web browsing, the list goes on. The issue with doing it this way is that VoIP traffic is incredibly time sensitive. It can quite often be the case that in using an existing service you will loose parts of a word or even whole words if it is bad enough. There are many factors that can contribute to this happening. Some companies have no problems at all doing just that, for others it simply won't work at all.
The only way to guarantee your call quality is to have a dedicated connection just for your Voice service. Think of it as phone lines rather than an internet connection. The best quality calls can be achieved when the connection is provided by the company that is also providing the VoIP connection. That way all the traffic is going directly from your network to theirs with no additional steps to add complications.
Getting these to work as two separate connections, one for Voice and one for Data will require an IT person who understands how to configure your router or firewall to send the right data to the correct link.