Yahoo! Messenger with Voice will work if any one of these TCP ports are open:

• 5061
• 443
• 80

At least ONE of these ports must be open in order to make PC-to-PC or PC-to-phone (Phone Out) calls, or to receive calls (Phone In).

If your connection to the web is through an http proxy, then you won't be able to make or receive calls with your PC.

Don't know if you're using a proxy? You can check by following these steps:

• Go to the Messenger menu in the upper left corner of your Messenger window, and select Preferences.
• From the Category list at left, choose Connection.
• Which button is selected? This will tell you your proxy status. The text below the buttons explains which button is most appropriate for your user environment. If you are behind a corporate firewall, please contact your network administrator for assistance getting around this issue.

Where's the Contact Customer Care button? With so many improvements to Messenger since the version you're using (lots more features and reliability), we figured you're ready to move up. So get your upgrade and with the new version, rest assured if you have questions, you’ll find that friendly button on its help pages.