No, it isn't true. You can use VoIP services on a Windows Vista machine. In order to fix the problems, I suggest you upgrade the utility to the latest version. Also, go to Start, type Windows Firewall and open the utility. Click Allow a program through Windows Firewall and then check the box next to ActionVoip.
After that, type Windows Firewall with Advanced Settings in the Search Programs and Files field and open the tool. Select New Rule from Inbound Rules, check the Port box, click Next, select All local Ports and follow the self-explained steps. Also, make sure that your security program doesn't block the connection.