Not a great help sorry but I enter my roster on the Outlook Calendar then just sync it to my phone although I don't have an iPhone yet this has worked with all my other phones.
One I have now is an N95 and it's ok on that.
I do remember though it won't let you do more than 6 months in advance or something like that, Outlook will only import a set amount of time, like a few months. I don't know any other way of doing it.
Have you had a word with your HR at work see if they can get the IT boys to produce something you can download?