Nobody wants to work on a project that is in the maintenance phase. But for software testers, this is an excellent learning opportunity for several reasons. The post is based on a remarkable book written by Chad Fowler, The Passionate Programmer.
Why is a project in the maintenance phase an excellent opportunity for software testers? First of all, you can use that system for black-box automated integration testing. As software is in maintenance, developers would be only assigned to resolve reported issues as cheap as possible. That means no unit testing, just hotfix code, and you to test it. Regression testing could quickly become a nightmare. As you are assigned to that project, you can offer to create automated smoke tests. Test that covers integration with external systems and critical functionality. Start with Ruby or Python, libraries that implement Http client or selenium, web driver.
The second opportunity is that you can quickly become someone that will know every bit of business process implemented by that application. You will know workarounds for issues that the project manager decided not to fix because of the restricted budget.
And finally, If you show that you care for the project in maintenance, your manager will put you on a list of recognized employees.