Here are the most basic steps to Configure Office365 on your iPhone/iPad:
- On your iPad/iPhone, under Settings, select “Mail, Contacts, Calendars” Add Account.
- Press “Microsoft Exchange” to add your new account.
- Enter your fully qualified e-mail name (eg. firstname.lastname@example.org) into both the Email and Username fields and your password. Click Next.
- The iPad/iPhone will use Office365’s autodiscover feature to fill in the server box. Click Next.
- You can customize the items that the iPad/iPhone will synchronize. Unless you’re doing something pretty unique, there is no reason not to synchronize them all.
Instructions from http://www.configureoffice365.com/