You can use WebApi with any client: JavaScript, Android, iOS, Windows App, etc. Any platform that can consume a web service will support Web API. So yes, Web API can be used in place of WCF. It is also much easier to setup and consume.
You can also pass/return server-side domain objects. By default, WebAPI serializes and deserializes using JSON, but that is configurable.
This is an example of WebAPI being consumed on Android:
http://hintdesk.com/how-to-call-asp-net-web-api-service-from-android/[
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You can learn more about WebAPI here:
http://www.asp.net/web-api/overview/getting-started-with-aspnet-web-api[
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