Default dialer on Samsung Galaxy S3
The Contacts app and the phone app work as one, however the contacts app should allow you to make a call using any app that uses the call broadcast receiver.

Ensure that the standard Phone/Dialer app isn't set as default:


Uninstall set default
Go into Settings-&gt;Apps-&gt;All-&gt;Dialer (or Phone) scroll down and select Clear Defaults.
Go back into the contacts app, and select a Contact to call. It should ask you which app you want to use. Select Go Dialer and select to always use that by default.