YAC.NET communicates directly with your modem to extract the Caller ID information. However, for this to work you need to subscribe to the Caller ID service from your phone company, and you need to have a modem which supports caller ID.
Modems come with commands that can be sent to the modem, and these are governed by a loose standard. However, different modem manufacturers decided on different commands to enable or disable the caller ID feature. Almost every modem comes with the Caller ID feature disabled by default.
This dialog gives you the opportunity to either enter the caller id enabling code (if you know it), or to let YAC.NET attempt to discover the code by trying some of the most common ones, and looking for the modem to respond with a success code.
When you hit “Start” YAC.NET will send the modem a series of codes, and look for an “OK” in response. When it gets an OK response, it assumes that this means that the modem recognized the code and that caller ID is now enabled. However, there are many brands of modems and some of them may accept the code, but not turn on caller ID. It’s very hard to test this capability because of the sheer number of modems. In addition, some modems will not support this feature, and so YAC.NET will not get a successful response, and will indicate this.
If YAC.NET indicates success after this step and still does not work, or indicates failure, try reading the documentation for your modem. Try to find out if it supports caller ID, and what code enables this feature.