JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately form tabs are currently not available in the facebook app. Here's a discussion regarding this issue: http://stackoverflow.com/questions/7220579/is-it-possible-to-show-a-facebook-app-as-a-page-tab-on-mobile-devices.
A possible workaround for this would be to use custom iFrame apps to embed the form to your facebook page. Simply follow this guide to setup a custom iframe tab: Adding a form to Facebook (Custom iFrame App).
They will provide you with a special Tab link for mobile devices.
Then, you can use that mobile Tab link as the Contact Us button link on mobile.