I use OWA for Iphone to access my University College London (UCL) e-mail account, and it works perfectly fine for me whenever I am on the go... And for the record, Exchange is an e-mail, contact and calendar solution for business/organizations, ergo requires a subscription and not compatible with Gmail, Hotmail..etc. So do not download it unless it is supported by your IT solutions.
Nate G.Y about OWA for iPhone, v1.0.7