You've said that twice on this thread. I honestly don't remember; is there a story somewhere? Wasn't there another company (Treo) also building hardware with Palm OS?
Handspring (later bought by Palm) and Sony were the most notable third-party vendors, although there were many others: https://en.wikipedia.org/wiki/List_of_Palm_OS_devices
Handspring (later bought by Palm) and Sony were the most notable third-party vendors, although there were many others: https://en.wikipedia.org/wiki/List_of_Palm_OS_devices