One should keep in mind that with VoIP your home network, router, and internet provider are all part of making internet phone work correctly. Quality Of Service (QOS)configuration and support in the router can ensure good quality even when your internet connection is handling other tasks.

If you have an ancient router, consider buying a modern one and learning how to configure it properly. I just got a Draytek Vigor 2130, and it has made quite a difference.

Good luck!