The Photosynth team is working on a version of the mobile panorama app for Windows Phone 7 due out after WP7's 'Mango' update in the last few months of 2011.
I do not think that waiting for a Windows Mobile 5 version of the app will result in anything besides disappointment. Any phone old enough to be running Windows Mobile 5 probably doesn't have the horsepower to do the live stitching, not to mention the motion sensors common in more recent phones like accelerometers + gyroscopes. There is also the need for a video function on the phone.
It is possible that if WM5 is not capable of creating panoramas, that it might be able to have a panorama + photosynth viewer written for it, but this will probably have to be done by someone besides the Photosynth team. Once the team releases their open source HTML5 viewer via the http://bit.ly/readwriteworld project , though, any WM5 developer should be able to port that viewer code to native WM5 code.