I would like to know if it is possible for me to view my hotmail messages on my iphone and for that message not to appear on my hotmail account when I sign in on a computer as I am having to delete the message twice
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Messages you delete on your phone will also be deleted on the server, so you shouldn't have to delete messages twice. Make sure you set up Hotmail as an Exchange account, not as a POP3 account, or the iPhone will just download a copy and will not push changes to the server.
If you haven't already, you can set up Hotmail as an Exchange account by going to your iPhone settings, then to "Mail, Contacts, Calendar", tap "Add account", and then go through the steps to set up Hotmail (if you have iOS5 or better, it will have Hotmail as an option.)
If you don't have iOS5 or newer, you will need to tap "Microsoft Exchange", and type in your Hotmail email address and password. (Leave Domain blank.)
Full instructions are available here: http://windows.microsoft.com/en-US/Hotmail/mobile?T1=t3&woldogcb=0