When you first open up Mafia Wars on your iPhone you are going to see a top graphical display, as well as nine options below that. Go ahead and find the Mafia Wars Options button, which is in the lower right hand corner. This puts the Options at the bottom of the left hand column right below News.
Once inside the Mafia Wars Options you are going to see a number of different things that you can do to change, each one that has a basic on and off switch. Through the Mafia Wars Options you can turn off and on sounds, the vibration in response to losing a fight, the vibrate when different points are regenerated back to full, the ability to receive an email to the attached email account for every Mafia Wars invitation, a weekly email about your Mafia Wars progress, and more emails about Mafia Wars news. Each of these you can simply just switch to off whenever you feel like. Once you do change the on / off setting you just hit the Done button at the bottom to ensure the action and bring you back to the main Mafia Wars home screen.