Here I am explain step-by-step
how to use WCF service and Linq to Sql in Windows Phone 7.
Go to the solution and add new WCF service application project.
Add a new item LINQ to SQL classes.
Go to the server explorer and add Database and drag the table
View Service1.svc in browser.
Add service reference to the project.
Type the url and go select service and click on ok.
Thank You....