Long press on any home screen (somewhere where there isn't an app or widget). When the "personalize" screen comes up, at the bottom is three tabs one of them says "sound"...go to it. Then tap "notification sounds"...now pick what ever sound you want for the notifications presented. Email is going to be your Exchange, Yahoo, Hotmail...basically anything other than Gmail. The option for "Message" is your text message alert. From what I can tell the only notification you can have for your Gmail is your "default notification"