Final answer:
Custom SOAP Web Service methods can be invoked from web applications, client applications, other web services, and enterprise integration systems using a variety of development tools that support SOAP requests.
Step-by-step explanation:
Custom SOAP Web Service methods can be invoked from a variety of environments, including but not limited to, web applications, client applications written in any language that supports web requests, and other web services. In a typical scenario, a SOAP request is formed following a specific XML schema (described in the Web Service's WSDL document) and sent over HTTP or HTTPS protocols to the Web Service endpoint. The service then processes the request and returns a SOAP response.
For instance, in a web application context, a developer might use JavaScript or server-side scripting languages such as PHP, Java, or .NET to create a SOAP client that sends requests to the Web Service. Development tools and integrated development environments (IDEs) like Eclipse, Microsoft Visual Studio, or NetBeans often provide built-in support for generating SOAP client code, considerably simplifying the process of consuming a SOAP Web Service.
Another common use is within enterprise integration, where different systems within a company communicate with each other using SOAP services. Here, middleware solutions like IBM WebSphere or Microsoft BizTalk Server can invoke custom SOAP services to perform complex business transactions.