Emarketer has put out its forecast for the growth of mobile Web usage in the US. The company is predicting 126 million users of the "mobile Internet" (begs for definition*) by 2013 from 68.6 million today. In September comScore said there were 198,378,000 users of the PC Internet in the US.

We agree with the 68 million figure today -- though access frequency varies. This almost 20% compound annual growth rate may be conservative, actually. Variables include:

• Data plan pricing
• Smartphone and quasi-smartphone adoption and penetration (driven by pricing too)
• WiFi and alternative access network development (for devices such as the iPod Touch)
• The "culture" in general (social behavior highly influential) 

Here's how it all looks today:

*Update: I just got this from eMarketer about the definition of the mobile Internet audience:

Mobile Internet users access the Internet from a mobile browser or an installed application at least once per month; excludes SMS, MMS and IM.