I am looking for statistics regarding what program(outlook, g-mail, yahoo, etc) is opening e-mails in the USA. We want to clearly understand what the e-mail looks like when it is delivered to different mobile devises.
As far as general statistics go, Litmus is a leader in that business- you'll get a great, up to date stats on the email client market share here. It'll be really easy to get lost in the wealth of information from Litmus.
We have a great article here that details some excellent stats on mobile emails.
Litmus is also a great tool for checking your email rendering in various email clients, including mobile devices. If you're serious about email marketing I'd highly recommend checking out their service to test your emails. We love it!