Rubicon Consulting's just published a report called "The Apple iPhone: Successes and Challenges for the Mobile Industry," based on a survey of 460 iPhone users. According to the research firm, the majority of iPhone owners are young, are loyal to Apple, having previously used Apple product, and are happy with their purchase.

Interestingly, while e-mail is the number one data function for the iPhone, it is mostly for reading not writing messages. So a third of iPhone users carry a second phone, usually a BlackBerry, either for basic voice calling or for other functions like…composing e-mail.

AT&T's benefited greatly by iPhone. The iPhone has increased its users’ monthly mobile phone bills by an average of 24 percent, or $228 extra per year. Half of all users switched to AT&T from another carrier just to use the iPhone. And, Overall, Rubicon estimates the iPhone has probably increased AT&T’s gross service revenue by about $2 billion per year.

Click here for more of Rubicon's findings.