Replace Servlet by Web Service

Here's the current scenario...
We have a servlet which receives params like account number, check number and responds by displaying a check image
We use certs for authentication, over a T1 line

Future Suggested Scenario : Replace the servlet by a Web Service and remove the t1 line

Issue is that the customer will not make any modifications to the way they invoke our servlet.

My question is... does it make sense replacing the servlet by an SSL based Web Service,
specially when the way it is invoked will not be modified.

Welcome to JavaRanch.

If the customer is unwilling to change the invocation, I'm guessing that he is also unwilling to allow changes to what he gets back. So what would be the advantage of changes to the implementation technology if the input and output stay the same?