A PDA is much like a smartphone without the phone features. This means no ear speaker, and no microphone for speaking into. I am sure one could make it a phone with a bluetooth headset, but this is not the role of the PDA. The PDA is intended to provide resources, and lighten the load of the smartphone. PDAs are not required, but some people might prefer them. For example, a PDA can have contacts that are rarely in communication. With that said, the phone can hold just the regular contacts, and leave the PDA for those occasional contacts. Another role will be that of a music player. Rather than draining the battery on the phone, the PDA can do music, and leave the phone for calls. There are a number of reasons why someone may want a PDA. It is not intended to be a replacement, but a compliment to the phone.