Are you talking about calling it from the Browser, or calling it from the JSP to render something in the HTML sent to the browser? Those are completely different problems.
If you're talking about calling it from a browser, the hot tip is to treat the SOAP payload as a big blob of XML boiler plate. Then fill in the few pieces of information necessary to distinguish the SOAP request, and then use an XMLHttpRequest to send the XML to the server. Finally you then pull the result from the SOAP return payload.
If you want to just call the web service from the JSP, the best bet is to make a utility wrapper class that wraps up all of the plumbing to make the web service call, and then call that wrapper from the JSP using standard Java technique.
Edit -- answering question
So, basically you have a index.jsp page with a text box. You hit submit, you want the text of that submit sent to a web service, and the result displayed back to the browser.
Simply, barring using the XHLHttpRequest, you want to create a Web Service Client (using JAX-WS, or Axis, or any of the other Java Web service tool kits).
Then you would have a Servlet or JSP take the the POST request from the form, extract the text from the request, and then it would call the web service. Finally it would render the result back to the client (using a JSP or whatever).
You can't POST an HTML directly to a Web Service, the protocols are different.
So
text text
| --> | | ----> |
| | Servlet |result | Web Service
| | | <---- |
Browser | | |
| | | forward |
| | | ------> | JSP
| |
| rendered result |
| <---------------------- |