I think Amazon said it best (http://www.amazon.com/gp/aws/sdk/main.html?p=APIReference/RESTRequestsArticle):

REST allows you to make calls to AWS by passing parameter keys and values in a URL (Uniform Resource Locator). AWS returns its response in XML (Extensible Markup Language) format. You can experiment with AWS requests and responses using nothing more than a Web browser that is capable of displaying XML documents. Simply enter the REST URL into the browser’s address bar, and the browser displays the raw XML response.

Can you test your SOAP service with nothing more than a web browser?