Hot on the heels of Apple's explosive Q1 2010 results come AT&T's Q4 2009 financials, and once again the iPhone helped its exclusive US carrier paint a rosy picture that includes 3.1 million new activations.

AT&T's fourth-quarter integrated-device growth included 3.1 million iPhone activations, the second highest quarterly total to date, with more than a third of the activations for customers who were new to AT&T. The average ARPU for integrated devices on AT&T's network continues to be 1.8 times that of the company's nonintegrated-device base.

ARPU (average revenue per user), as Dieter keeps telling us, is the magic number for AT&T, and despite complaints about service in cities like New York and San Francisco, iPhone users continue to use -- and pay for -- a lot of data.

And with Apple still in their corner, and the iPad plans so far exclusively on AT&T as well, that may not be changing soon...