I want to use the phone jack in my basement to connect my Vonage phone adapter in order to distribute the service to all phone jacks in my house. But I need to convert it to the "main" jack in order for the Vonage signal to be distributed. I was told I should be able to convert this jack to the main one as they are wired in parallel.

http://support.vonage.com/doc/en_us/649.xml?docid=69

After you isolate from outside, connect to the closest/easiest jack.