Microsoft Service used by both ASP.NET and PHP websites

Question

Hello Friends,

I have a SQL Server Tables and use Microsoft Tools (Visual Stuidio C# and ASP.Net) to develop web functionality. There is another group that I work with that  that uses php and they would like to use some of the functionality I have created  in there site.

I cannot give them direct access to the database but can provide a service they could call. I feel that WCF has more overhead  than we need but certainly is an option.

My Question is what are some other options that I could provide and what are the pro's and con's of each one with your preference.

Thanks in advance for your input.