If your fritzbox came with your internet package, it will probably have configured a predefined SIP server. Thus, when making a telephone call, your router establishes a connection with your internet provider SIP server silently. The conversation takes places using VoIP.
You can configure the fritzbox to use a different VoIP server, or what is even better, several servers. When making a call, you will be able to select which one to use just by dialing a prefix. In this article I explain how to do this.
If you have a DSL connection and you often make cellular or international calls, you should be aware of the VoIP technology and some providers that could make an enormous difference on your monthly bill.
This is my first blog entry in the Internet after many hours learning *ml's, dbms's, cms's, os's... The list is far too long and boring to be included here.
Definitely, "interneting" has a very high learning curve due to the many different technologies that are involved. Fortunately, creating new content once you have learned the basics and have a good working environment set-up, is fairly easy.