Goggle’s recent purchase of AdMob for $750 million sent a clear signal that big players are getting serious about mobile advertising. As I wrote recently in ClickZ, despite the beginnings of mobile consolidation and the rich investment the giant made, it may be premature to declare 2009 “the year of mobile.”

Google bought AdMob for a lot of reasons. AdMob is a clear leader in the mobile ad space, which is projected to finish 2009 at $416 million, a growth rate of 30% YOY according to eMarketer. The purchase fits in to what seems to be Google’s expansion plans for both CPC text link media and display inventory. Etc., etc. The investment makes sense from a bunch of different angles.

But here’s one that I haven’t seen many people talk about: as of August 2009 the iPhone made up 40% of the ad requests across AdMob’s network. They serve ads into a bunch of popular iPhone applications as well as a wide variety of mobile web sites. That is a treasure trove of consumer behavior data that Google can use to fuel future developments in Android, the Android Market, AND with the rumored Google-branded phone. Combine AdMob’s iPhone data with Google’s own application data and insights from Google services like Google Analytics, Google Maps, and many other popular Google web services accessed heavily by iPhone users, and suddenly Google has perhaps the clearest vision into what iPhone users are doing outside of Apple and AT&T.

Not a bad way for Google to keep an eye on what it likely views as the #1 competitor for it’s own mobile offerings.