While the iPhone is still an entirely different beast worldwide, Apple and Google’s main fronts are in the United States, and a shift has occurred (and, thankfully, we’re not talking about plates within the earth’s crust): Android has taken over the iPhone’s US install base (as was predicted by an AdMob mobile metrics report that gave us a similar preview). NPD Group is reporting that – in Q1 2010 – Android has become the second-most installed smartphone OS in the United States with 28% market share – coming just beneath RIM’s Blackberry OS (enjoying 36% of the market share).

iPhone OS, on the other hand, currently sits at 21% in third place. I’d imagine that the US smartphone market is very important for all of the vendors, and Android’s proving that it can hold its own against the iPhone and – soon – possibly Blackberry. Executive director of industry analysis for NPD Group, Ross Rubin, says:

“As in the past, carrier distribution and promotion have played a crucial role in determining smartphone market share. In order to compete with the iPhone, Verizon Wireless has expanded its buy-one-get-one offer beyond RIM devices to now include all of their smartphones.”

With RIM, Microsoft, Apple, and Nokia all set to release new versions of their OS, Palm hoping to make a comeback with HP pulling their strings, and new operating systems seemingly popping up every day, the smartphone war will only get crazier from here and – as Phandroids – it’s great to see that Android has more than just a fighting chance.

[Thanks, Phonescoop!]