There was an attempt to port csharp-sqlite to Windows Phone, and its output was a project called wp7sqlite,
http://wp7sqlite.codeplex.com/
It was active in 2010, but now it is dead. Why? Well, please check out csharp-sqlite and read its source code carefully. Yes, it already has built in support for Windows Phone. Kudo!
http://code.google.com/p/csharp-sqlite/