Until now, I am able to consume some WS using SOAP in my Android application (with kSOAP2 library), but as I read JSON is more lightweight than XML and Android offer native support for JSON Web Services, I am wondering if is it possible consume the same WS using JSON?
Or it should be made some changes on the server side?
The server side will need to produce a JSON output — something that many REST services will do. So yes, the server side will need to change. SOAP is XML – there is no way around that.