OS X Puma (10.1) and Jaguar (10.2) Dialup Walkthrough: Step 3

Ensure that your Port Configurations are the same as shown here.
-If it isn't at the top now, drag "Modem Port" by the name to the top of the list.
-Click the checkbox next to "Modem Port" to activate it.
-If you will not be using "Built-in Ethernet," or don't know what it is, uncheck the check box. (Provided that it is already checked.)