I actually made a port of taiko no tatsujin for the WP7 platform and used osu mapcharts for the testing phase. Whether or not I would consider pushing this further is something I'd have to consider personally. In all honesty i feel that the phone platform is rather limiting for something like Osu! Standard (mostly due to the screen size / resolution) though following that microsoft has apparently got some magic up its sleeve for the next version of the mobile OS (that it will better support porting between ARM (metro), desktop and Phone) I feel it may be possible to develop something for that "ecosystem".
Either way, it's good to know someone is interested in a windows phone port. If enough people request it then i'd probably go ahead and mock up a playable beta just for fun. In the meantime I'll leave you with the only ingame screenshot I have of the taiko port :3 (note the scoring, combos, naming and pretty much everything was just placeholder rubbish... needless to say this was an extremely quick mock up, nothing more)