Quantcast released its latest report of mobile Web usage by OS in North America on Monday and it showed a big jump for Android, and a significant dip for iPhone.

As you can see in the chart below, in terms of the share of mobile devices that access the Web, Android OS is up on on monthly, quarterly, and annual basis. Meanwhile, Apple iOS (the new name for iPhone OS) is down on a percentage basis over all three periods. RIM’s BlackBerry OS was up for the quarter but down on a monthly and yearly basis, and all other smartphone platforms combined were down as a percentage for all three metrics.

In terms of the trend line, you can see iPhone slowly ceding some of its commanding lead since January 2009, while Android has been on a consistent climb since the release of the Motorola Droid and the Android 2.0 OS in October 2009.

Still, when you look at the overall picture, Apple iOS devices (iPhone, iPad, and iPod Touch) have a larger share of mobile Web consumption than all other mobile devices combined, and nearly triple the amount for Android. That said, these numbers were also released before two new very popular Android devices–the HTC Incredible and the HTC EVO 4G–have fully impacted the market. Apple’s iPhone 4 will certainly challenge those two devices but there are now Android smartphones on all four major carriers in the U.S. while the iPhone remains limited to AT&T. That will continue to allow Android to outflank iPhone until Apple takes it to additional carriers.