The people at Rubicon Consulting undertook a survey of iPhone users in order to know more about their characteristics, and I suppose to know more about the iPhone phenomenon. It surveyed 460 randomly selected US iPhone users.

Announcement: http://mobileopportunity.blogspot.com/2008/04/announcing-new-survey-of-iphone-users.html

Summary Findings: http://rubiconconsulting.com/downloads/whitepapers/Rubicon-iPhone_User_Survey.pdf

Business Related Findings of the Survey
The survey produced some interesting User Experience tidbits (see below) but it was much more informative about business issues in the mobile industry. Here's some stand out mobile industry findings.

• Almost half of iPhone users switched cellular carriers in order to get the iPhone. Wow! Subscriber churn is one of the key metrics in the carrier business.
  

• The iPhone increases mobile browsing. About 75% of iPhone users say the device has lead them to use more mobile web browsing.
  

• The iPhone has increased its users' monthly mobile phone bills by an average of 24% or $228 per year.

• The iPhone is expanding the smart phone market. The survey found that about 50% of iPhones replaced a conventional cell phone (by conventional cell phone I would guess they mean a non-touch screen device that does not have a full keyboard and does not specialize in email).

• About 28% of iPhone users said they sometimes carry an iPhone instead of their laptops.

All of the above statistics clearly indicate that (a) the AT&T move to get the iPhone exclusively was a good strategy in terms of subscriber churn -- it has driven an increase in the number of subscribers; (b) the iPhone is a successful smart phone and is being used for email & web browsing and may well force other handset manufacturers to make these and all tasks easier and more appealing; (c) The new model of handset manufacturers getting a slice of monthly subscriber payments has been established -- I am very curious to see how that plays out.

User Experience Findings of the Survey
In terms of User Experience here's what stood out to me about Rubicon's survey.

• Reading Email is the #1 function of the iPhone. A whopping 72% of iPhone users read email on their phones every day. An additional 11% do it occasionally. Composing email is a bit less popular with about 58% doing it daily. As the Rubicon report points out this isn't that surprising since the iPhone lacks a physical keyboard.
  
  But it also points out a fundamental of mobile user experience: composing anything (an email or an Excel spreadsheet) on a small device will happen less frequently than reading the same data. People will put up with a lot to communicate with other humans (see text message composing) but in general users will compose documents on computers, and when they are mobile they'll want to read these documents on devices.
  

• The fact that 75% of iPhone users have increased the amount of mobile browsing also stands out from a UE point of view. Everyone knows that the mobile browsing user experience is absolutely atrocious! It's slow, it's expensive, normal web pages do not layout correctly, and WAP is a sad alternative that features hyper-links but no interesting content other than news articles.
  
  The report also notes that 40% of iPhone users reported web sites that do not display correctly. Even so, the layout engine and zooming feature (with it's associated multi-touch gesture) both are clearly UE gains over previous mobile browsing designs
  

• One of the more intriguing User experience questions suggested by the study centers around the finding that most iPhone users appear to be early adopters, Mac enthusiasts and/or technology savvy users. They are also younger, with 50% being under the age of 30 and 16% are students.
  
  So, does this take anything away from the much touted ease of use of the iPhone? In other words could the iPhone not be as easy to use as has been said? After all early adopters, technology savvy users and students should all find it easier to use any product than the general population would find it to be.
  
  My take is that the ease of use of the iPhone may be slightly over rated because it has mostly been used by power users so far. Users with less education and less technology sophistication would probably have a harder time learning the device than today's iPhone users.
  
  However! The iPhone user experience has a couple big things going for it. First of all it is a simple device compared to other smart phones. It has less features than say Nokia Series 60 and so those features are easier to find. Have you looked recently at all the items in a series 60 menu? It's amazing that anyone can find anything.
  
  The second factor is the enthusiasm for learning that any iPhone user has because of the magical and theatrical nature of the iPhone user interface. If you've talked to anyone who's owned one of these devices then you know how excited they are to own one and learn everything about it. For those that may not know, average users can overcome big usability issues if they poses enthusiasm and a willingness to experiment and learn.

• Finally it is interesting to note that 10% of iPhone users reported hand pain at some point during their ownership of the device. To me this points out an interesting thing about the large touch screen of the iPhone. I think touch devices can have higher ease of use than conventional phones because any UI object is directly manipulable (and therefore users don't have to go searching for functions that may be hidden in menus or invoked by a random hard key). However, users have to move their fingers and hands all over the device as interactive elements can appear anywhere on the large touch screen.
  
  Compare that to a typical Nokia device with 5-way key, two soft buttons and an ITU keypad. Users of those devices don't have to move their hands nearly at all, and in fact can easily operate their phones with one hand (if say they are pushing a shopping cart or even driving a car).
  
  Many mobile user experience experts think touch screens are the wave of the future. They clearly will have a large part in mobile UE going forward, but it's important to remember that conventional phones have advantages too.