Global Android ad impression share has surpassed iPhone OS for the first time, according to a new report by independent mobile ad network InMobi.

The report revealed that although iPhone OS and Android both continue to capture share on a global basis, over the last few months Android growth has been increasing and has now surpassed that of iPhone OS.

The report highlighted that Android smartphones are becoming a primary gateway to digital content, as the platform provides consumers with many device options, at varying price points — creating a real alternative to the desktop or laptop.

In addition, many households across Asia, Eastern Europe and Africa rely on Android smartphones as the primary platform to consume media instead of a web-based PC.

The report highlighted that total mobile advertising impressions on the InMobi network grew by 21% (December 2010 to March 2011), driven by the large influx of smartphone impressions, which increased by 2.8 billion during the period.

Mobile phone manufacturers Samsung, Apple and HTC continued to capture share from global leader Nokia. Although Nokia still remains in the number one position with a 40% share of global impressions.

Nokia lost -3.9 share points in 90 days, while Samsung (+1.6 share pts), Apple (+1.9 share pts) and HTC (+2.8 share pts) gained share.

Globally, 35% of all mobile ad impressions now occur on smartphones.

The smartphone segment grew by 50% in North America in the last 90 days, with three out of every four mobile impressions in North America is now on a smartphone.

iPhone OS captured +9.7 share points in March 2011, following the early February launch of the Apple iPhone on Verizon Wireless in the US.

Although iPhone OS enjoyed a boost with the Verizon launch, Android captured +4.0 share points and leads iPhone OS by 5.2 share points.

The aggressive growth of Android has moved the phone manufacturer HTC into second position with (+6.1 share points) and 2.2% share of impressions.

InMobi North America vice-president and managing director Anne Frisbie said as expected, the introduction of the Apple iPhone on Verizon has given the iOS platform a big boost against the recent Android swell, although it was not enough to retake the top position.

"With both platforms having strong support, the most interesting story of 2011 will be to watch what happens to Windows Phone 7 and Nokia," Frisbie said.