The extraordinary growth of Google's (GOOG) Android phones can be traced in six months of smartphone advertising data from Millennial Media, the largest independent mobile ad network.

In a series of pie charts, they show Android overtaking Research in Motion's (RIMM) BlackBerry between July and August in ad impressions, gaining rapidly on Apple's (AAPL) iPhone between June and September and finally coming even with iOS in October with a 37% share apiece.

But an interesting thing happens in Millennial's November report, released early Tuesday. It shows Android and iOS tied for the second month in a row, at 38% each.  After six months of breakneck gains, we have something that looks like equilibrium.

Apple is still the No. 1 smartphone manufacturer, as it has been for 14 months in a row, but there are signs that the iPhone is approaching saturation in the developer community. In a Millennial survey, Android was the No. 1 platform developers plan to support in 2011, with Microsoft's (MSFT) Windows Phone 7 and the iPad tied for second. The iPhone was relegated to fourth place, after the BlackBerry.

Below: Six months of Millennial pie charts.

Source: Millennial Media

If you were planning on popping a lot of location-based ads into your upcoming killer iPhone app, you might want take a peek at the latest update from Apple for developers. A rather stern note on the site reads: “If your app uses location-based information primarily to enable mobile advertisers to deliver targeted ads based on a user’s location, your app will be returned to you by the App Store Review Team for modification before it can be posted to the App Store.” Is Apple doing this to prevent abuse from advertisers, so that users won’t end up with advertisements from stores all around them? There isn’t any real explanation as to why this isn’t allowed, but it’s certainly worth taking note if you’re building an app with the intention of putting advertisements in. After all, you wouldn’t want to spend your precious time building an app only to find out that it will be rejected by Apple, right?

Interesting little tid bit. Somewhere else folks have been wondering out loud if this has anything to do with Apple's purchase of Quattro or some other secret juicy soon to be released nugget? Unfortunately I don't recall where or who was doing this wondering...

It certainly can't be about diluting the App Store right? It is already flooded with loads of sub-quality apps... so what is this about?

Or I may be wrong. Perhaps they are just trying to clean up and tighten control to prevent users from being spammed with ads...

Regardless of the underlying reason why Apple is doing this it is for the good of the industry. It does make one feel protected and looked after doesn't it?