Paid applications began appearing in the Android Market a week ago, but so far they aren’t selling well. It’s not clear if that’s because Android users aren’t used to paying for apps or if there’s simply a lack of good apps in the Market (the most notable app so far is one that costs $200 and does nothing). Well, here’s a cool paid app that you may want to check out.

The online phone number directory WhitePages has launched a paid version of its Caller ID app. When you get a call on your Android phone, Caller ID pops up with information about who’s on the other end of the line. Obviously, all of us have our contacts saved on our phone, but for calls from numbers you don’t know, Caller ID accesses its database of over 600 million numbers and immediately sends what information it has to your screen so you can decide whether or not you want to answer.

The service also offers alerts that pop up when the call is from a known telemarketing number. And it has a reverse look-up feature for unknown numbers that you miss calls from or that text message you.

This all sounds great, right? The downside is that the app costs $6.99 for six months of use. While a lot of users may not be used to a subscription fee for apps, that’s really less than if you used 411 once a month over that span, as WhitePages notes on its blog. And if you really don’t want to pay for the app, there has been, and will continue to be, a free version of Caller ID in the Android Market that lacks some of the comprehensive look-up features. That free version has already been downloaded over 100,000 times.

WhitePages also has an iPhone app, but because apps cannot run in the background on the iPhone (an ongoing problem), a service like Caller ID wouldn’t work. So on the iPhone, the app basically just functions as a look-up tool.

Want to see the Android app in action? Watch the video with the bumpin’ music below.

[youtube https://www.youtube.com/watch?v=icWly1fmqSA&hl=en&fs=1&color1=0x2b405b&color2=0x6b8ab6]