Unfortunately, DIDCALL Dialer servers are down and you can't use the application anymore. As an alternative, I suggest you try a similar utility from the Software Informer database. Personally, I recommend you use Skype, FreeCall or Ventrilo. All of them have the same main features like DIDCALL Dialer, are free to download and install and can connect with a mobile phone or another PC that has the same software installed.
