One of the big differences as far as PDAs go is that they required a stylus, and the touch was pressure sensitive. It couldn't be used just with your fingers.
The iPhone's touchscreen implementation was innovative. I remember quite a lot of debate in the period between the iPhone's announcement and release about weather or not a capacitive touchscreen on a phone would provide a terrible experience. There were a lot of very smart people out there who thought it just wouldn't work (greasy fingerprints came up a lot). At the time, for Apple, putting this kind of UX out there was a huge risk, and a major innovation in the industry. They really nailed it, and in hindsight it, like many other great innovations, seems obvious, but at the time it was far from it.
EDIT - here's a quote from a CNET article at the time:
"11. Just how useful is the touch screen? The iPhone user interface looks elegant, innovative, and easy-to-use, but is it the best interface for a device like this?
Whenever you do anything, the iPhone will command your full visual attention. "No buttons" may be sexy, but it also means you can't do anything without looking at the phone.
The iPhone's iPod usability may suffer even worse from the touch screen. Have you ever tried to operate an iPod while it's in your pocket? You can do it, but it's hard. The iPhone will make blind iPod-surfing downright impossible.
That said, it looks like the iPhone will eliminate accidental pocket-dialing once and for all."
The iPhone's touchscreen implementation was innovative. I remember quite a lot of debate in the period between the iPhone's announcement and release about weather or not a capacitive touchscreen on a phone would provide a terrible experience. There were a lot of very smart people out there who thought it just wouldn't work (greasy fingerprints came up a lot). At the time, for Apple, putting this kind of UX out there was a huge risk, and a major innovation in the industry. They really nailed it, and in hindsight it, like many other great innovations, seems obvious, but at the time it was far from it.
EDIT - here's a quote from a CNET article at the time: "11. Just how useful is the touch screen? The iPhone user interface looks elegant, innovative, and easy-to-use, but is it the best interface for a device like this? Whenever you do anything, the iPhone will command your full visual attention. "No buttons" may be sexy, but it also means you can't do anything without looking at the phone. The iPhone's iPod usability may suffer even worse from the touch screen. Have you ever tried to operate an iPod while it's in your pocket? You can do it, but it's hard. The iPhone will make blind iPod-surfing downright impossible. That said, it looks like the iPhone will eliminate accidental pocket-dialing once and for all."
http://news.cnet.com/8301-17938_105-9677208-1.html