Smartphones may not be as suited for gaming as traditional handhelds from Sony and Nintendo, but that isn't stopping iOS and Android from dominating the mobile games market in terms of revenue. According to a new study by Flurry Analytics, 58% of income from portable game software in the U.S. during 2011 came from iOS and Android devices, up from 34% last year. Meanwhile, Nintendo's DS is down form 57% in 2010 to 36%, while Sony's PSP holds a 6% share.

That's a big turnaround from 2009 when Nintendo's DS and Sony's PSP owned 70% and 11% of the market, respectively, while iOS and Android held a 19% share combined. Unfortunately Flurry Analytics doesn't break down market share numbers for Apple and Google's platforms individually, but if their estimates hold true, we can conclude that smartphone gaming sales have surpassed their more traditional counterparts for the first time.

A number of factors have contributed to this phenomenal growth, such as the high adoption rate of new smartphones and tablets, the convenience of carrying a single device, and the super cheap prices for quality titles compared to those for dedicated portable gaming systems. The fact that titles created with touchscreens in mind tend to be easier to handle for casual gamers likely also contributed to the rocketing growth of smartphone gaming.

Meanwhile, the lukewarm launch of the  3DS certainly hasn't helped Nintendo's cause and Sony's PlayStation Vita is not expected to arrive in the U.S. until February 2012 for $249 (Wi-Fi) or $299 (3G and Wi-Fi).

Flurry estimates total revenue on the portable gaming market will reach $3.3 billion in 2011, of which Nintendo will grab about $1.2 billion and Sony another $200 million. It'll be interesting to see how Nintendo will counter the threat of smartphone gaming. Flurry suggests it'll have to consider difficult choices such as divesting its hardware business and distributing content through non-proprietary platforms, but Nintendo's president Satoru Iwata has stated unequivocally in the past that creating games for smartphones was "absolutely not under consideration."