Looking at your web.config serviceModel section, I can see that you need to add a webHttpBinding and associate an endPointBehavior that includes webHttpGet.
Your operation contract is correct. Here’s how your system.serviceModel config section should look in order for you to be able to consume the service from a GET HTTP request.
<system.serviceModel>
<behaviors>
<serviceBehaviors>
<behavior name="MyServiceBehavior">
<serviceMetadata httpGetEnabled="true" />
<serviceDebug includeExceptionDetailInFaults="true"/>
</behavior>
</serviceBehaviors>
<endpointBehaviors>
<behavior name="WebBehavior">
<webHttp />
</behavior>
</endpointBehaviors>
</behaviors>
<services>
<service behaviorConfiguration="MyServiceBehavior" name="MyService">
<endpoint address="ws" binding="wsHttpBinding" contract="IMyService"/>
<endpoint address="" behaviorConfiguration="WebBehavior"
binding="webHttpBinding"
contract="IMyService">
</endpoint>
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
</service>
</services>
</system.serviceModel>
Be sure to assign a different address to your wsHttpBinding endpoint, otherwise you will get an error saying that you have two endpoints listening on the same URI.
Another option is to leave the address blank in the wsHttpBinding, but assign a different address to the webHttpBinding service. However, that will change your GET address as well.
For example, if you assign the address as “asmx”, you would call your service with the address “MyService.svc/asmx/MyMethod?MyParam=xxxx“.