Its a long time since I used dial up, but may be if you pick up the receiver on your phone whilst connected to the internet through your wireless set up you should hear the noise that dial up makes on the phone line.
Or on the computer you're using with the wireless receiver, if you look down in the right hand corner of the task bar at the bottom of your screen you should see an icon for a radio receiver with a coloured light flashing on it. Right click on this and it should take you to the set up for your wireless connection. It should tell you somewhere in here which connection you are using.