Update #1 13/03/2013, here is new blog about Tiled WMS overlay for Windows Phone 8 :http://blog.sumbera.com/2013/03/10/tiled-wms-overlay-in-windows-phone-8/
I have quickly tested my new Windows Phone 7 (Samsung Omnia) device with the Czech cadastral map WMS overlay over the BingMaps and DeepEarth (also see this blog here: http://blog.sumbera.com/2010/11/10/wms-overlay-on-bing-maps-vs-deepearth-on-wp7/) . if you are familiar with www.ikatastr.cz and iPhone version of it (iKatastr) than this example is using same data sources.
In short : it was a great experience – WP7 was smoothly registered, automaticaly connected to internet even without a SIM card using USB cable and Visual Studio 2010 integration just works perfect (so far:) In comparison to many difficulties and ‘certification hell’ on iPhone this is a great relief. Now giving the fact that Nokia is going to support and develop Windows Phone 7, great user experience with WP7 and (for me and menay others) great development experience, this might change the mobile landscape significantly over the 1 or 2 years.
I will guess here that WP7 platform will exceed number of iPhone applications in less than 2 years.
Update #2 Reviewing this after 2 years (March / 2013), – something went wrong with this estimation, but do you remember Gartner predictions from that time ? for example here : http://www.globalnerdy.com/2012/05/07/the-windows-phone-predictions-that-idc-gartner-and-pyramid-research-probably-hope-youve-forgotten/
but we are not yet in 2015, so we will see.
Update #3 02/2016 : this estimation was completely wrong , Windows Phone platform is nowhere, looks like great lesson learned – even you own great language and framework (C# and .NET) there is nothing that guarantees you being successful on emerging/disruptive platform/form factor. Objective-C (then Swift) or Java on Android got this mobile cake.