Here’s some news that will surely make hardcore Android fans squirm: The Verizon iPhone has helped the iPhone 4 maintain its lead as the single best-selling smartphone in the US in the first quarter of 2011. Meanwhile, Android saw a dip in sales for first time in two years, according to the NPD Group.

Android’s steady lead couldn’t last forever, and clearly the iPhone is a greater threat now that it’s on Verizon. It’ll be interesting to see how Android holds up in the next few quarters as hype for the iPhone 5 builds up but more killer Android device are introduced throughout the year.

The data comes from NPD’s “Mobile Phone Track” service, which tracks smartphone purchases from consumers over age 18 (but doesn’t include enterprise phone purchases).

Overall, Apple’s iPhones grabbed 14 percent of smartphone sales in the first quarter, which ranked it third behind Samsung (with 23 percent of the market) and LG (with 18 percent).

Smartphone sales increased by 8 percent, while total handset sales fell by 1 percent. NPD says that this past quarter is the first time smartphone sales outpaced sales of other mobile phones with 54 percent of sales.

Android sales fell for the first time since the second quarter of 2009 to 50 percent, down 3 percent from the previous quarter. The iPhone OS’s share of sales jumped 9 points to 28 percent, while BlackBerry, in its unstoppable free fall, went down 5 points to 14 percent.

The biggest surprise from this data was Android’s sales drop, but personally I don’t suspect that will continue for much longer. Apple’s sales bump was all about pent up demand from Verizon users, and Android likely won’t face significant competition again from Apple until the iPhone 5 lands.