Go to "Prefs" Under the system category. then go to Sound % Alerts. from the drop down menu at the top choose "Phone" as the application you would like to adjust. then make sure the volume is set to something other than "Off" you can also set if it vibrates or not here.
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Go to "Prefs" Under the system category. then go to Sound % Alerts. from the drop down menu at the top choose "Phone" as the application you would like to adjust. then make sure the volume is set to something other than "Off" you can also set if it vibrates or not here.