I'd given up on it, but FileMaker has now released a $20 FM Pro companion for the iPhone (and iPad!) -- FileMaker Go. It requires iOS 4. The available documentation is in a technical brief.
It does NOT support synchronization. You copy FM 7 (7!) or later files to the iPhone. It can be a client to a FM server database. From the tech brief it looks like it could be an application development environment (scripting).
It does NOT support encryption. Your data is only as protected as the phone itself; you can't assign a secure password to your password database, for example.
If it had encryption, I'd buy it.