But according to AdMob, one of the largest mobile Web ad networks, Apple’s (AAPL) handsets now dominate mobile Web traffic in almost every category.

According to AdMob’s analysis of the billions of ad requests it saw in January:

• The iPhone OS now represents 51% of U.S. smartphone traffic, leaving RIM’s (RIMM) BlackBerry (19%) and Microsoft’s (MSFT) Windows Mobile (14%) in the dust.
• In the global handset market, the iPhone and iPod touch now represent 18.3% of worldwide ad traffic — second only to Nokia (NOK) with 30.1%
• Worldwide requests from Apple devices grew 28% month over month to 1.2 billion in January.
• The iPod touch is rapidly catching up to the iPhone; it now represents 40% of Apple requests, up from 20% in September.

AdMob stores and analyzes every ad request, impression and click from more than 6,000 publishers’ sites in over 160 countries every day, according to its website. Its January analysis of all that traffic, issued Thursday, is available here.