Yes, you can read PDF eBooks on a Palm OS devices device using Adobe Reader for Palm OS v3 or higher. You must first download the eBook to a PC or MacOS X computer using Adobe Reader and then transfer to the PDA.
Get Adobe Reader for Palm OS here
Get Adobe Reader for Pocket PC here
Get Adobe Reader for Symbian OS here
iPhone offers free apps, you can locate them by search under "Free Apps" search for ereader, ebook, or kindle.