You need to evaluate what you want from the phone.
For corporate/business communications Windows 7, Android and iPhone in about that order.
If you like Apple stuff and apps, the iPhone is a good bet if you don't mind some of its quirks, like having to hack it to be able to use your own ringtone...
Android has really turned into something incredible but be careful because some Android phones don't ship with the most recent version and some phones have a much better skin and more intuitive menu system than others, so check out comparative reviews if Android honks your hooter.
Windows 7 hooks straight into any version of Exchange for business class emails on the hoof (which is why I like it) and ships with MS Office if you need to use it (I do) and a drop dead easy to use interface. There are fewer apps available for Windows 7 but that gap will close over time.
In short, if you already have an Apple Mac or love iTunes on Windows to manage your music (why on earth that would be the case is beyond me, but it takes all sorts) then the iPhone is a good bet with loads of apps.
Android phones also have a ton of apps and you can do a lot of tinkering with the phones themselves.
Windows 7 just works - it does what it does very, very well, with fewer apps available and zero tinkering possible.
I have a Samsung Vibrant (Galaxy S on T-Mobile to you and me) running Android as my main personal phone, and an HTC HD7 and Samsung Omnia, both running Windows 7 for work purposes.
I run several dozen iPhones for various business clients and the problems they bring to the table are a real ball ache. They work best as standalone domestic phones and, for my money, both Android and Windows 7 offer a much better business choice. Put an iPhone in a typical Microsoft business environment and they are pretty awful by comparison to either Android or Windows 7, hence my suggestion to look at what you intend doing with the phone first, and then narrow down suitable kit based on your requirements.
There is always the Blackberry route as well...
Good luck whatever you decide on.