According to AdMob, a firm that serves ads to mobile phones, the iPhone is the No. 1 mobile device in the world. But what does that really mean?AdMob tracks mobile Internet use. It collects data from more than 6,000 mobile Web sites and Web-based applications, analyzes it all, and releases findings based on that information in the form of reports. AdMob just released the results of its October report.

Since July, when the iPhone Apps Store -- and applications in which AdMob places ads -- launched, AdMob saw huge growth in the iPhone's presence around the world. AdMob says that there are almost 400 iPhone applications that display ads from AdMob. In October, AdMob's advertisements were seen on more than 4.5 million iPhones. AdMob says it can determine an individual iPhone by a unique identifier that is composed of various hardware properties such as the device serial number. This identifier is guaranteed to be unique for every device. That's all a fancy way of saying that AdMob is sure about its numbers.

Some other tidbits buried in the report are fairly juicy. AdMob says, "The top 10 devices worldwide, in order, are the Apple iPhone, Motorola Razr V3, Nokia N70, Motorola Krzr K1c, Motorola W385, Nokia 6300, Nokia 3110c, Nokia N73, Motorola Z6m, and RIM BlackBerry 8300." Interesting to note that there are really only three smartphones on that list. The rest are feature phones.

AdMob also reports that, "Sony Ericsson passed Motorola to become the No. 2 handset manufacturer worldwide. Apple jumped ahead of LG and RIM to become the No. 5 handset manufacturer worldwide." How can Apple be the No. 5 five handset maker, but have the No. 1 device?

Keep in mind, these figures aren't related to sales of the devices. Rather, these figures tell us how much these devices are used.

Bottom line? The iPhone is the No. 1 phone in the world when it comes to viewing advertisements. It is not the No. 1 device worldwide in sales. The iPhone's "No. 1" status does, however, speak volumes about how the device is being used.