Apple iPhone users make mistakes more often when texting compared to users of phones with hard keys, a new study found.

User Centric tested how many mistakes mobile phone texters make, comparing the results of iPhone users with customers who have phones with full keyboards and those with numeric keyboards. User Centric, a Chicago usability consulting company, studied 20 users in each group.

The study, while based on an extremely small sample size, makes for interesting reading.

The researchers found that while iPhone users entered text as fast as their counterparts, they made significantly more texting errors. iPhone users made 5.6 errors per message, while keyboard users made 2.1 mistakes per message and numeric phone typers made 2.4 mistakes.

The iPhone has only one key. Users type text messages on a keyboard that appears as an image on the phone's screen.

Surprisingly, the study found that iPhone texters don't improve with experience. The researchers also asked users in the other groups to send text messages using the iPhone. These novice iPhone users made mistakes at the same rate as people who have owned iPhones for at least one month, the study found.

The iPhone only recently hit shelves in Europe, where mobile phone users have been texting longer and more often than their counterparts in the U.S. The mass market in Europe has been using numeric keypads to text for years and has been largely resistant to change, with many phone users shunning predictive text programs or other texting innovations.

But Apple isn't the first to introduce a new kind of mobile text-entry system. Digit Wireless has been pushing its Fastap technology since 2001. Fastap is a combination of hardware and software technology that lets phone makers place more keys on a tiny keypad by using raised and lowered keys. The phone maker can choose what letters and numbers go on the keys and how many keys will appear on a phone.

Despite its novelty, Fastap is receiving a positive reaction in Europe, said Mark Connon, CEO of Digit Wireless, speaking during the recent CTIA Wireless I.T. and Entertainment conference. "The iPhone is driving the user interface discussion," he said.