Actually Nokia is pushing pretty hard for an instagram port to the Windows phone. The Finnish company just released their own version called "#2InstaWithLove." It's poorly thought out and pale in comparison however.
To be honest, I wouldn't even bother trying it. If you like the Windows phones, go ahead and get one. I don't think one app would make that much difference. You could always put the pics on your PC at a later time and use instagram from there.
Or, wait until it DOES get released for the Windows phone. Shouldn't be too terribly far off in the future. Up to you really.