Is ErikEJ hints at, sql is on the device and is used by the built-in applications and OS ... however it s not exposed. If you watch one of Charlie Kindel s talks at MIX10 and keep watching for the questions at the end he mentions this. He hints that it s something that they want to look at exposing in the future, but they didn t have enough time to do so in this release.

Anyways, unless you live/work in a place with spotty coverage, I think that the device will have connectivity more often than not. Because the user will either be in wifi range, or on the 3g network. I know that it s very rare that my iPhone doesn t have data connectivity. So you can probably rely on having access to a cloud service somewhere.

No - as Windows Phone 7 Series is "consumer oriented" there will be no SQL Server Compact Edition.

If you agree with me and some developers you can try posting in SQL Compact Edition in WP7? and request support for it. However, I don t think they will change their opinion...

There seem to be some people trying to migrate SQLlite to WinPhone7Series and someone posted a link to Siaquodb (never heard about it before) which seems to work but is not free.

Even if you don t have access to the cloud there are many ways to store data on the device. Unless you re doing an enterprise level app (and why would you on a device targetted at consumers, not enterprise users) you could take your pick on solutions. LINQ to XML is a good possibility.

Look for an upcoming release of the Sync Framework to support offline data caching for Silverlight applications on Windows Phone 7 and Silverlight on the desktop/browser. While this isn t SQL CE, it does offer a technology to support synchronization of data between SQL Server in a data center and data on a Windows Phone 7 device. As Liam Cavanagh mentions in this blog post before TechEd:

I have a TechEd session this week where I will be demonstrating all of this as well as how we will be extending the capabilities of the sync framework for creating offline applications, specifically allowing Silverlight, Windows Phone 7 and even non-MSFT platforms to be used for the clients.

Link