Nokia has made their online Maps website off-line enabled, but not for Windows Phone.
Now iPhone, iPad or Android (2.3) devices can point their browser to m.maps.nokia.com, and get maps and routing. The maps can however also provide voice directions by pre-loading up to 2 MB of voice data, which can then be used off-line. The service only works for walking directions.
When one tries to visit the page with a Windows Phone however you get a screen explaining â€œOur Nokia Web app has not been optimised for your device.â€ Nokia Maps, which is free for all Windows Phones, does not provide voice directions.
It seems, rather ironically, Nokia is happy to promote their services for iPhone and Android, but not to allow non-Nokia Windows Phones to gain the benefit of them. So much for enhancing the whole ecosystem.
Read more at Nokia Conversations here.