According to InMobi’s latest Insights Report (January 2012, North America only), Apple’s iOS has regained the market lead previously held by Android with a 35 percent share in ad impressions in the US and Canada.

That’s a 12 percent bump compared to the 23 percent market share InMobi says iOS had in October 2011, according to the report.

InMobi bases its reports on data from its own network, which it says serves over 93.4 billion monthly mobile advertising impressions worldwide, and points out that Android held the lead for most of last year.

In North America, InMobi’s available ad impressions exceed 55 billion.

The company argues that the recent surge in ad impressions on the iOS platform likely has to do with the success of the iPad and the iPhone 4S. In fact, InMobi says the top three handsets for January 2012 were Apple devices.

It’s worth noting that InMobi rival Millennial Media also just released a report on mobile ad impressions, claiming Android’s share increased by 504 percent in 2011.

We’ll keep watching these market share fluctuations closely.