In the past Apple have not given an easy way to use your Hotmail account on your iPhone.
I read a while ago that Microsoft had given Exchange access to their hotmail accounts and I tried it but it did not work. I tried once again and now (for me at least) it works 100% now.
So how do you get your Hotmail account on your iPhone? Well its easy!
Go to http://www.unlockit.co.nz/hotmail.mobileconfig from Safari on your iPhone and it works.
It will ask for your username twice (put in email@example.com in both times) and then it will ask for your password and it is as simple as that.
Your Hotmail mail will now be available from your iPhone Mail application