15% of E-mail is Viewed on a Mobile Device [infographic]
According to Litmus.com research, as of July 2011, 15% of all e-mail is viewed using a mobile device.
What’s also pretty neat is that the iPhone accounts for 10% of all email viewed. That’s virtually a parallel number to Hotmail and Yahoo! Mail, and more than double Gmail.

Source [Litmus.com]