I've used a PDA and a phone for years, and like them separate. Each is small and practical. I update each as it's worth doing so. (Bluetooth is essential!). The phone is "current", the PDA 2 years old but still does all I want it to.
My daughter (gadget freak) bought one of those phone-and-PDA devices. She got rid of it quickly and went back to separates. As Richard says, it didn't do anything oustandingly well.
Horses for courses!