I've been using Seven for all my email accts including my work email as well. Seven is the company that made Sprint Mobile Email Work.
As far as I can tell there is no limit to the amount of email accts that you can push to your phone. I have my corporate, hotmail, yahoo, and 3 earthlink accts pushed at the same time. Best of all, it's FREE! So I really love it.
For your corporate, you can either use the desktop connector or OWA. The site is:
http://community.seven.com Try it I absolutely love it and if you have a problem their techs usually respond within 1 business day.
Hope that helps.