I would like my iPhone app to get dynamic content off the net. This content should be managed using a CMS. I would like to know in particular if I can setup Drupal or Joomla or
You can also take a look at StorageRoom, which is a CMS for Mobile Applications.
Disclaimer: I created this myself to scratch my own itch.
Wordpress with the JSON-API plugin is a great solution, especially if you need a web site as well.
You can find a good example here that uses Wordpress and Phonegap to get a basic app going.
This seems to be a very promising solution!
Apache Usergrid
I have briefly tried DreamFactory for some trial project but never got around to using it in production. Usergrid seems to be in the right direction in providing a full fledged solution (which can also work for modern web apps)
If you can access the content in any serialized format (e.g. XML or JSON), it should be no problem to use any CMS as a "backend" for your application.