In a classic case of a well funded incumbent buying a start-up to gain control over a quickly developing market, mobile advertising provider AdMob has announced it's entered into a definitive agreement to acquire the assets of AdWhirl.

AdWhirl, an in-app advertising aggregator for iPhone apps, launched in April 2009, and raised $1 million in seed funding in June.

It claimed to be serving around one billion ads per month via iPhone and iPod touch apps for over 1,000 developers. CPM raters were reported as being around $1.90.

AdWhirl's selling point was it enabled developers to switch dynamically between different ad networks. Ironically, it supported AdMob, alongside the likes of Quattro Wireless, Mobclix, VideoEgg and JumpTap.

Financial terms of the agreement were not disclosed, but the price could have been as much as $10 million.

AdMob said it would expand on AdWhirl's platform to create enhanced developer tools that will be offered as an open source mobile ad mediation solution. This will enable developers to allocate their inventory among multiple mobile ad networks and maximise their fill rate.

"AdMob's number one priority with this acquisition is to help maximise monetisation opportunities for app developers and publishers," said Omar Hamoui, AdMob's CEO.

"By offering this first ever open source ad mediation solution, our goal is to provide a much needed open, unbiased and transparent tool for mobile publishers who would like to build financially rewarding businesses that are fueled by advertising."

AdMob currently serves 7.1 billion mobile banner and text ads per month, and, in total, has served more than 100 billion ads across a network consisting of more than 7,000 mobile sites and 3,000 apps.