Foursquare map is working on older device (3597) like map without roads, only POI's. And it contains much more POI's then main map.
It can works as standalone map (POI over basemap roads) and with NT maps (mix of NT and FS POI's).

But 3597 doesn't show any additional POI infos and don't have special FS icons in search windows.
May be in future releases of firmware?