Summary:

Monthly figures out today from mobile ad network Millennial Media indicate that the mobile network that is benefiting most of all from the s…

Monthly figures out today from mobile ad network Millennial Media indicate that the mobile network that is benefiting most of all from the smartphone data explosion is not a cellular operator, but the collective power of WiFi.

Millennial’s data for month of July, which measures activity based on ad impressions in the U.S., notes that a full third of all traffic came from WiFi networks — which include those from mobile operators but also the many hotspots and networks that are not.

The strength of WiFi on the network is a sign that — despite the efforts being made by operators to firm up data caps and to try to stem the tide of mobile data price wars against competitors — consumers are still finding workarounds by often shunning cellular networks altogether.

But that’s not to say that mobile networks are not driving any mobile data traffic: the next-biggest network contribution in terms of activity came from Verizon, at 19 percent of traffic. Within that, smartphones made up just over half of the devices being used, but it’s notable that most of the rest are “connected devices,” which can range from tablets to internet-enabled portable game players and connected portable music players like the iPod.

Platforms versus devices. At 61 percent, Android is still the largest collective OS on the Millennial network, but this seems to mainly come from the sheer number of device makers using the platform, rather than the dominance of any single OEM driving traffic. Apple’s iPhone, as it has in past months, has continued to take that crown. In July, Apple (NSDQ: AAPL) accounted for 26.45 percent of all traffic, with the iPhone at 13.6 percent.

If there is one Android maker that is making a strong impression in the rankings (pardon the pun), it is Samsung — which comes in second place in the manufacturer rankings at just over 19 percent of all impressions; the Samsung Nexus S is its most popular device, with 5.73 percent of all impressions. What’s less clear is how Android breaks out from other platforms that Samsung uses: the others include its own proprietary OS, Bada, as well as Microsoft’s Windows Phone 7. It’s worth pointing out, though, that in the device rankings, neither Bada nor WP7 appear among the most popular devices:

Indeed, Microsoft’s platform is still miniscule on the network — only two percent of all impressions, the same as Nokia’s U.S. disappointment, Symbian — but remarkably that comes after the platform has grown by 71 percent over the last month. That means Windows Phone will need many more months of the same kind of growth (or ideally better) before it hits the big time. It seems to be making that start: just yesterday, it was announced that Windows Phone 7 has 30,000 apps on its store.

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