Windows 7 Mobile edition
Oh god, I can imagine it now....
Press Power Button, wait for 5 minutes for windows to power up and install the updates you hadn't noticed the phone had downloaded on your data plan costing you the equivalent of a small country's annual turnover.
Let windows load, only to find that the phone driver wasn't recognised and is now listed as 'unknown device'
Reboot again to get the device to work and then try to make a call. The problem being that the device still hasn't completed booting.
Decide to phone your mobile provider and sort out the settings for SMS, only to find that SMS settings isn't available to people with the Windows 7 Home Premium Mobile edition, only to users of the Business or Ultimate edition, of which you can only upgrade to the Ultimate edition from Home Premium.
Purchase and install the Ultimate upgrade, set the phone up and enjoy using it, resolving never to let it go flat as it takes 2 full batteries just to boot the phone.
Move on 2 months, your mobile bill looks suspiciously like the number for an american premium rate phone sex service. You investigate and find that 30 viruses (virii?) have infected your phone from your home PC and have been spamming iPhone users with 'buy cheap online prescriptions' emails and that all your contacts, including the hot blonde you met at the club the night before now dial guatemalan minicab firms first.
No good can possibly come of this.