If the mobile device apps are going to move to API V2.X then they will need to use OAUTH. This requires the re-direct via a browser to grant access to the client application. This means you need to actually be able to display the grant access page on the device.
Currently this page is not suitable for display on small form factor devices. There needs to be a mobile version of the page. This can be done using browser detection.
Ideally there should be a mobile version of the site for those users who haven't installed a client yet.