The word from Flickr is that "a very high majority of the globe will be represented by Nokia’s clever looking tiles." ("Clever looking?") But more cities will be built on OSM data. The blogger calls it Open Street Map; it's really OpenStreetMap. Twenty-two cities use OSM and a few are using a new style (look) built on TileMill/MapBox.
StreetInside thinks this is a big deal since Yahoo is not using data frm Google or Apple or Garmin (the lattter two of which do not have their own data!). Yahoo has been using Nokia/NAVTEQ data for Yahoo maps for some time.