Reactivating Voicemail after dialing #004# on iPhone

I was new voicemail so I was finding ways to turn it off. After reading a few articles I found of that dialing #004# on the phone app temporarily stops it. I was happy with the resolve but now that its no longer active I'm felling the necessity of Voicemail. How to I revert the effects of Dialing ' #004# '. Help me out guys!!!!!!!!!!

[Re-Titled by Moderator]