We reported earlier that '4th & Mayor' is now the default Foursquare app for Windows Phone. Technically, that is true, for now.

We just got word that in fact a new, official version of Foursquare is coming to Windows Phone and it's something other than '4th & Mayor' (which may be going open source, according to developer Jeff Wilcox). Not much can be said at this time nor any time frame, but here is the bit from Microsoft on ISVs:

...Over the last year, we have discovered and learned from many of you that Windows Phone 7 is a great leap for Microsoft. In the spirit of this, foursquare will soon unveil a new foursquare mobile app that will take advantage of some of the unique capabilities, features, and experience for Windows Phone 7.

Until then, we encourage you to explore a great foursquare application, built by a 3rd party developer, called 4th and Mayor. It includes rich functionality like photos, comments, new leaderboards, the Explore feature! Download it today by visiting https://foursquare.com/apps/ and clicking on the Windows Phone logo in the upper right corner of the page.

Keep up the enthusiasm, keep up the dedication, and we will continue to keep you posted as we continue to develop the new official foursquare mobile app for Windows Phone 7.

So it sounds like they're building it from the ground-up and are really looking to leverage the unique abilities of Windows Phone to make this new Foursquare app truly impressive. Question is, the bar is set so high with '4th & Mayor'--can they really improve upon it?

Source: Microsoft on ISVs (Blog); Thanks, Russell Clark, for the heads up