From the promo video below we can see that Ping will support Gmail, Aol, Yahoo, and iCloud mail.
Robert Scoble was given an early look at the app and he says, "This is subtle but huge. I think this is going to be one of the hottest consumer apps to come out in the fall." Scoble also declared, "This blows away Mailbox and the Gmail app."
Ping is set to launch this month. You can get on the waitlist at the link below...