DailyTech has been reporting on Google's meteoric rise in smartphone market share for quite some time now, but we didn't expect to hear the numbers that are coming from the NPD Group today with regards to Android's place in the hot sector. NPD says that unit sales for Android-based devices bolted past Apple iPhone devices for the first quarter in the U.S.

According to NPD, Android-based devices accounted for 28 percent of the smartphone market while smartphones running Apple's iPhone OS garnered just 21 percent of the market. Both, however, were well behind RIM which still commands 36 percent of the market.

"As in the past, carrier distribution and promotion have played a crucial role in determining smartphone market share," said NPD's Ross Rubin. "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."

It should be noted that there are numerous Android-based smartphones on the U.S. market compared to relatively few iPhone models. When it comes to the Android sector, there are many choices including the Droid, Droid Eris, Nexus One, Backflip, and the Droid Incredible (which wouldn't be accounted for in NPD's numbers) among others.

The iPhone, however, is only currently available as the 8GB iPhone 3G (the last generation model) along with the 16GB and 32GB iPhone 3GS.

In addition to the wealth of differing smartphone designs on the Android side of things, users who pick Android-based phones have a number of wireless carriers to choose as well including Verizon, T-Mobile, and AT&T in the U.S. Apple's iPhone, however, is artificially limited to AT&T's network fresh from the factory -- you can, however, unlock the iPhone using a software hack and use it on T-Mobile's network albeit without 3G connectivity.