The mobile industry is growing and changing fast. Here are some recent statistics about this area:

• At the end of 2007, there were 255.4 million U.S. mobile phone users. There were 207.9 million at the end of 2005 and 109.5 million at the end of 2000.
  
• 138 million people used SMS in the first quarter of 2008. 82 percent of wireless customers under the age of 24 use SMS, but 50 percent of SMS users are age 35 or older.
  
• 69 million people accessed mobile WAP sites in the first quarter of 2008. This is the fastest growing mobile area currently.
  
• 15.8 percent of U.S. households are wireless only. In 2005, just 8.4 percent of U.S. households were wireless only.
  
• U.S. wireless customers used 2.1 trillion minutes of air time in 2007, up from 1.5 trillion in 2005 and 533.8 billion in 2000.

Sources: Limbo via the Mobile Marketing Association and CTIA – The Wireless Association

The following charts are courtesy of m:metrics. Both charts display detailed data on the mobile phone market (as of Q1 2008) for the United States and several other countries. These charts include information on the use of the mobile Web for news/information, use of text messaging for news/information, smartphone penetration and more on mobile phone usage. 
 

Click image to enlarge

Click image to enlarge

Additional Resources
The following resources are from the Mobile Marketing Association (MMA), the Interactive Advertising Bureau (IAB), CTIA – The Wireless Association and the World Wide Web Consortium (W3C).

• Advertising Guidelines – mobile advertising principles (MMA)
  
• Advertising Overview – platform status report and how-to advertising information (IAB)
  
• Code of Conduct – guidelines for mobile advertising and marketing (MMA)
  
• Coupons – an introduction to mobile coupons (MMA)
  
• Glossary – mobile terms and definitions from the Mobile Marketing Association
  
• Mobile Search – an introduction to mobile search (MMA)
  
• Statistics – wireless facts and figures(CTIA)
  
• WAP Code Guidelines – guidelines and tests to check for basic mobileOK compliance for user experience (W3C)