Microsoft threw away a lot of features when they moved from Windows Mobile 6.5 to Windows Phone 7. The discusions on this topic that you’ve heard probably focuses on Windows Phone 7’s lack of copy/paste and multitasking. However, Windows Phone 7 lost a number of other features and abilities available in its predecessors: Tethering, Bluetooth keyboard support (from 3rd parties), and the ability to install software outside of the Windows Phone marketplace are just a few. One of the big missing capabilities that has gotten very little discussion outside of the developer world has a big impact, however. Windows Phone 7 shipped without database support. This essentially killed apps for vertical markets that required the phone to have a local database.
Redmond Developer reported, however, that Microsoft’s Joe Belfiore stated in his MIX keynote last week that the Windows Phone Mango update scheduled for sometime late this year will include a built-in SQL database that developers can use.
In the meantime, Windows Phone 7 is unable to support apps that require relatively sophisticated database operations and storage.