Troubleshooting Yahoo Messenger Voice and Video connection issues
It is possible that the video and voice features are unable to function properly because of a conflicting issue with your computer system or internet connection. This could be caused by software on your computer (antivirus or security software), issues with your Local Area Network (LAN), or issues with your Internet Service Provider.
Unfortunately, Yahoo is not able to control or diagnose technical issues outside of our network. If you have a firewall blocking Yahoo Voice you need to open up some outgoing TCP connections. Note that it is the outgoing connections that matter, not incoming connections. In most firewalls, you have to specify a destination port or port range to open.
Yahoo Messenger uses ports 5050, or 443, or 80.
Even if you don't use a firewall, your Internet service provider (ISP) might use a firewall, a network address translator (NAT), or a proxy server that blocks voice traffic. Any of these could prevent you from using the PC-to-PC voice feature in Yahoo Messenger. Please contact your ISP's network administrator for assistance getting around these issues.
You can also contact your antivirus and security software vendor for further Troubleshooting assistance.
In many cases, it is a good idea to have your firewall and proxy configuration and settings information available when contacting your ISP. Please click here for further assistance with configuring your firewall and proxy settings.