There are many reasons for which the Voice Call button is/becomes grey, so inactive. The main reason is the team of software programmers Yahoo has these days. I had the same problem. Voice Call worked fine until one day I just found it grey. Skype worked fine. The "Setup Video and Voice" test was fine, still no Voice Call capability. In my case, it turned out that the YIM changed randomly the connection type. Go to the command bar, Messenger/Preferences/Connection. By default you see the "Connect directly to the Internet" check. However, it might be an illusion, the YIM might actually work with the "Connect via a proxy server" option. Check willingly the "Connect via a proxy server" option, then Apply. The check back the "Connect directly to the Internet" option and Apply. Indicating the correct type of connection (Dial-Up, Broadband, High-Speed) might help. This solution solved my problem. I hope it'll help those many user facing it.