So what might keep Symbian users with Nokia and entice them to switch to Windows Phone?
One of the main things could be preloaded Nokia maps that can be used offline.
In fact, it's my understanding that Microsoft might have the option to offer Nokia maps on other Windows Phones too.
So the timing seemed interesting, given those first Nokia Windows Phones might be coming end 2011/early 2012.
Nokia (Ovi) maps have always been able to be used off line and already come standard on all Nokia smart phones with the country of sale pre loaded including free turn by turn navigation. Map sets for other countries can be loaded free of charge. I don't see the WP7 devices being without Ovi maps and other Nokia feature otherwise that will drive away current Nokia owners.
Yes, I think you're right about the possibility of Ovi maps being loaded on other WP7 phones. Certainly from my understanding the deal between Nokia and Microsoft, gives Microsoft access to Ovi maps for it's Bing search engine.
What also might entice Nokia owners to stay with Nokia is the imminent release of at least one phone with the Meego platform. Very interesting timing on that to with the release of the WP7 devices.