The ascendency of Android as the operating system of choice for new customers in the US appears to come directly at the cost of both Apple’s iPhone and the BlackBerry. Just released Nielsen research data shows that, over the last six months, the popularity of phones running Android has taken off.

Since the beginning of this year, new Android phone purchases have continually increased in terms of market share, from 6% in Q4 of 2009 to 27% now.

At the same time, sales of new BlackBerry (39% vs. 33%) and iPhone (34% vs. 23%) devices have decreased as a proportion of total new purchases. This means that Android comes out second to BlackBerry in share of newly purchased smartphones when broken down by operating system, passing the iPhone on the heels of what can be described as a meteoric rise.

BlackBerry still leads the total smartphone marketplace, as the OS is being run on 35% of all US smartphones, vs. 28% for iPhone and 13% for Android.

It’s interesting, Infosecurity notes, that this news about Android piggybacks on two recent trends affecting the smartphone industry. RIM, maker of the BlackBerry, is facing bans by Middle East governments over its strong security features, which makes monitoring communications difficult, versus that of the Apple iPhone, which has the reputation of being a less robust device from a security perspective.

This reputation, however, may be softening a bit, as analysis from Forrester Research said that recent enhancements to iPhone operating system security has this device ready for deployment by businesses and other organizations.

And the Android smartphone OS is not without its security critics. Google has said it performs background checks on application developers operating in its open-source software market place Android, but last week’s news about an app that transmits data back to a server in China has put Android security in question yet again.