Sounds like you just need to invite those users into QuickBase. QuickBase is already web-based and if a user accesses it on a mobile device, they will be taken to the mobile version of your application. While the interface for mobile isn't the best at the moment, I know that QuickBase is making every effort to bring it up to today's mobile standards. Additionally, you can build a stand-alone mobile page that you can host on your website's servers that can interact with QuickBase in the background if the standard mobile experience doesn't work for your users.
