LINQ and WCF Services

Question

Hi all... I have queries about LINQ ..

I have one application and 3 databases -
1st  database - for developers
2nd database - for testing team
3rd database - for users (production)..

In normal 3-tire architecture, if the database credentials changes, then we change the connection string in web.config file.

But, in LINQ, Once the .dbml file is included, it makes datacontextclass itself...

SO, in future, what to do so that only the connection string is changed and rest all code remains the same ??

Also - please guide on - how to use WCF Services with LINQ-to-SQL - i.e. all LINQ Queries in WCF Services so that the portal runs smoothly and faster in IIS Server.

Please guide !