You can expose the service in two different endpoints. the SOAP one can use the binding that support SOAP e.g. basicHttpBinding, the RESTful one can use the webHttpBinding. I assume your REST service will be in JSON, in that case, you need to configure the two endpoints with the following behaviour configuration

　　An example of endpoint configuration in your scenario is

so, the service will be available at

Apply [WebGet] to the operation contract to make it RESTful. e.g.

public interface ITestService{   [OperationContract]   [WebGet]   string HelloWorld(string text)}

Note, if the REST service is not in JSON, parameters of the operations can not contain complex type.

Reply to the post for SOAP and RESTful POX(XML)

For plain old XML as return format, this is an example that would work both for SOAP and XML

[ServiceContract(Namespace = "http://test")]public interface ITestService{    [OperationContract]    [WebGet(UriTemplate = "accounts/{id}")]    Account[] GetAccount(string id);}

　　POX behavior for REST Plain Old XML

　　Endpoints

Service will be available at

REST request try it in browser,

SOAP request client endpoint configuration for SOAP service after adding the service reference,

　　in C#

TestServiceClient client = new TestServiceClient();client.GetAccount("A123");

　　Another way of doing it is to expose two different service contract and each one with specific configuration. This may generate some duplicates at code level, however at the end of the day, you want to make it working.