if you set yourself up with SIP or IAX phones (soft phones or hardware) you can register those phones directly to the system via the internet or local area network.
once that is done, the call to the agent from the phone system is an internal call, not billable by anyone.
then you ONLY pay for calls generated to prospects.
obviously this only applies if you have SIP / IAX phones that can directly contact your vicidial server.
A little research on Asterisk, descriptions of similar systems such as Trixbox and FreePBX based systems will probably help you to understand HOW this technology works.
Another method would be to grab the nearest P4 laying around in your office (unused agent workstation? no need for a monitor after it's built! just a CPU with a network card!) and install Vicibox 3.0.6 (available at Vicibox.com right now for free!!!). After you've followed the installation instructions, you'll have a functional system that can make calls as long as you have internet. The number of calls is related to the speed of your internet ... but the "TEST" can be done on virtually any internet connection so you can understand the system.
If you are curious, i REALLY recommend that method of learning. It's quite helpful.
If you don't want to wipe that machine and use it, there is even a Demo CD that you don't even need to install. Just boot from it and you have a functional (for testing at least) Vicidial system, capable of making and taking a couple calls at a time. But fully functional (old version, though, but still works very well for testing and look/feel is the same).