I would look into the MS Sync Framework. I do not think Mobile 2005 is supported but if you can go with CE 2008 it could be an option.

http://msdn.microsoft.com/en-us/sync/default.aspx
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1610640&SiteID=1

>We are writing an application for Windows Mobile 2005 (or higher) that utilizes a SQL Server CE database using C#.
>We wish to synchronize the CE database with our SQL Server database on a work station once an ActiveSync connection has been established.
>Before we develop our own utility to synchronize the two databases I want to make sure a tool does not already exist.
>
>Can anyone provide some insight on best practices for synchronizing a SQL Server based application from a PDA to a server?
>Thank you!