Remember we have the old Apps issues.
The stock apps on iOS and Android are less than what you had on the PalmOS. While we can start looking at the usual iPod Touch with that slide out add on keyboard, you have a lot of work to find replacement apps of the caliber you had on the PalmOS.
Finally there are non Android models that have the slider keyboard and are not a phone. You don't have to get the phone service to use the machine.