> How can i detect comm port which is connected to modem.<br><br>Well one method is to open the comm port. Then you need to know how modems work to talk to the modem.<br><br>If you want to know specific information about any of these issues please ask specific questions. If you don't know anything about any of it then you need to find some resources that discuss these technologies and start reading. You are not going to write a modem application in VC in 4 lines of code.<br><br>There are plenty of information and sample code resources in MSDN for working with the Win32 COMM API's. There might even be some for working with the Hayes modem AT command set, but different modems have there own extensions to the Hayes standard so depending on what you need to accomplish you might need to consider that.<br><br>Then of course Windows supports the Unimodem interface through the TAPI SDK, and there is always the RAS API under most Win32 systems. These may or may not be relevant to your problem since you have not specified what it is.<br><br>"But, that's just my opinion... I could be wrong".<br>-pete