The obvious answer is to see if you can get the data from somewhere else. If its proprietary information to their app, then you may be stuck there. If that's th

The obvious answer is to see if you can get the data from somewhere else. If its proprietary information to their app, then you may be stuck there. If that's the case, I'd ask yourself whether its something you should really build. Let's assume you do, since it would be cool, and you're happy making it a non-commercial product to be able to keep using the API—if you can add other features/connections/data sources that make a commercial offering compelling and less dependent on a single source of information that in all likelihood will want to cut you off, then you may be able to make it work, and might be an attractive acquisition for the company whose data you want to use. But i'd make sure you don't invest too terribly much in the effort. As Fred Wilson has pointed out, never fill holes in someone else's product.