AdMob, in its monthly report on mobile Web use, said today that Apple’s iPhone is now the fourth-ranked phone for Web access around the world. Motorola’s RAZR, the Nokia N70 and Motorola KRZR are ahead of it.

In total, there were 5.1 billion requests per month for advertisements to AdMob’s network in September 2008, the company said.

The full report is available for free.