Thank you for your post.
If you are on the same Wi-Fi network, FileMaker Go can access a file hosted by Filemaker Pro (Advanced) and make live changes. Also, if your iPhone has 3G coverage, then you log in as a guest via the IP Address of the machine hosting the file.
If you don't have network coverage, you can use iTunes to copy the file to your iPhone. If you make changes, then you'll have to copy the file back to the Mac. There is no sync option.
There is no sync option, but it might be possible to create a FileMaker script that uses Import Records to synch the data for you--that might be easy or difficult depending on the number of users and the number of tables in your system.
Thanks to both answers. As one of only two users, the import script would work to fetch data from the iPhone. The iPhone user has FMPA at hand, but the iTouch user makes most updates.