Officially, Google wants users to upload all data to their web services, then download to the Android-powered smartphone. Apple, on the other hand, wants you to export from Palm Desktop, import everything into Windows Mail or a similar desktop app, and then use iTunes to synchronize the content with the iPhone.
However, there are third-party apps, such as The Missing Sync and CompanionLink, that help bridge the gap. I prefer the former, but the latter is especially good at handling Palm Desktop migrations.
Hope this helps,