Can someone tell me what the difference is between a smartphone and a pda?

The differences between the two have become blurred. Years ago a PDA was nothing more than an electronic organizer, and cellphones only had basic electronic organizer functions.

A modern Personal Digital Assistant (PDA) is like a handheld computer. PDAs often run PocketPC or the Palm OS, include wireless networking connectivity, and can be loaded with various kinds of programs. For example, Windows Mobile includes Microsoft Mobile Office, allowing you to access various types of office files, as well as Outlook. You can also download applications to the device, or load databases into the device, and use them wherever you take your handheld.

A SmartPhone brings the computer-like functionality of a modern PDA into a cellular phone. Some models also bring the functionality of an MP3 player.

SmartPhones are great when used primarily as cell phones. If you start using them more for their applications or as an MP3 player, the battery life takes a hit and you're left with little talk time on the phone.