The neatest new app I've seen in a long time is a simple idea inspired by the messy patchwork of mobile handsets, work phones, and personal landlines all of us juggle every day. It's called GrandCentral, and it gives you a single phone number through which you can screen and route all your calls. It also records voice mails for easy access via a Web interface or on your mobile handheld.

Sound confusing? Well, GrandCentral's path to "One Number" (their term) nirvana is a little circuitous. Here's the deal: You actually get a new phone number, which becomes your "One Number. . .for Life" (their term again, and it's trademarked, buddy). What you do is give this number out to all your contacts.

Then you set up your GrandCentral account, via its Web interface, so that incoming calls to that "One Number" ring either your cell phone, work phone, home landline, or all three. This way, you're reachable wherever you happen to be. As well, GrandCentral effectively gives you a single-point caller ID, so you can screen all your inbound traffic.

The best part is that GrandCentral handles all voice mails, recording them for playback via its Web interface, or even on your mobile phone. I was afraid my very corporate BlackBerry 8700 wouldn't support GrandCentral Mobile, since its documentation doesn't let on that it can handle MP3 files. Sure enough, though, GrandCentral voice mails played back on the BlackBerry, albeit at pitifully low volume.

As well as being a killer mobile app, I think GrandCentral is brilliant in its obviousness. You want to give yourself a V8 whack in the head when you realize that nobody thought of this before.

The two guys who pulled it all off are Craig Walker, the former CEO of VoIP vendor Dialpad Communications, and Vincent Paquet, Yahoo's director of business development for voice comm. They founded GrandCentral in 2006, and sold it to Google this July, so you could say that Walker and Paquet have just won the Web 2.0 sweepstakes.

GrandCentral's Web interface manages playback of voice mail messages. (Click picture to enlarge, and to see 2 other GrandCentral screen grabs.)

GrandCentral is still in beta, and usage right now is by invitation only. It's currently free. Eventually, GrandCentral will emerge into commercial mode and attempt to charge for its service. Then we'll see if it's a supportable business, though of course Google could prop it up for eternity, or at least until the Web 2.0 bubble bursts.

In real-world usage, there are a couple of stumbling blocks. The main impediment to making GrandCentral one's main comm tool is that it's very difficult to get people who already have your cell phone number to start using your new GrandCentral number. What ends up happening is, the latter is foisted off on second-tier business contacts -- people you meet at shows or salespeople/customers who you prefer to screen because you don't much want to talk to them anyway. (I didn't really just write "customers," did I? We love those folks.)

Personally, I found that I ended up using GrandCentral not as much as I would have liked, because of the aforementioned number-conversion conundrum. Possibly, it's simply that I'm not important enough, because I don't have the hundreds of daily inbound calls required to make this really efficient.

That's why, like that guy on TV who puts his Social Security number on the side of a truck and dares people to steal his identity, I'm going to publish my GrandCentral number. It's (646) 248-6723. And remember, I'm screening.