GrandCentral is a service which, if it lives up to first impressions, will solve the biggest annoyance of life here in the 21st century. It's a unified messaging system that gives you a single phone number, which rings at least three phones -- your work phone, home phone, and cell phone -- simultaneously, whenever someone calls. GrandCentral also has nifty voicemail-management and call-screening features.

I've seen other services like this before, some almost 10 years old, but they were all wicked expensive, and generally only available by arrangement from specific phone service providers. GrandCentral is aimed directly at consumers; it's currently in free beta and, when it rolls out, will reportedly cost $15 $9.95 per month.

When someone calls you, GrandCentral answers the phone, and tries to identify the caller through the magic of caller ID. If it recognizes the caller, it rings through to you and lets you know. If it doesn't know who the caller is, it asks the caller to state his name, and then it rings through and lets you know.

Update, 6 pm EST: GrandCentral e-mailed me to clarify the previous: If your caller has Caller ID enabled, GrandCentral asks for their name once. After that, whenever you get a call from that number, GrandCentral uses that announcement to let you know who's calling.

GrandCentral has a great Back to the '80s feature: Remember how, when we all used answering machines instead of voicemail, you could screen your calls by listening to people leave a message? You can't do that with most voicemail, but you can with GrandCentral. You can listen on your phone while the caller leaves a message, and then, if you want to take the call after all, touch a key and you'll be connected.

You can record your call at any time by touching 4.

GrandCentral helps with telemarketer calls -- you can designate some callers as "spam," and, if someone calls from that number again, GrandCentral won't even ring your phone.

GrandCentral lets you set up rules for how to handle different callers. It users Caller ID to identify individual callers and add them to an address book and, once that's done, you can tell GrandCentral to route some callers through to different phones, send others to voicemail.

Here's a feature I like: Switch phones in the middle of a call by pressing *. All of your phones ring, and you can pick up the one you want. No more, "Let me call you back from a landline."

GrandCentral has its own voicemail service, which you can check by phone, e-mail, or Web.

The user interface is extremely simple and easy to use. Looks like a lot of effort went into designing a tool that'll be effortless.

TechCrunch has a nice write-up, including on-target discussion on lock-in. Once you're deep into GrandCentral, are you stuck? The answer, unfortunately, seems to be mostly yes -- if you want to quit, you can't keep the same phone number, and there's no way to export your online address book or saved voicemail messages. Update: GrandCentral says they'll help you transfer your phone number if you leave their service, although ultimately, of course, it'll be up to your new provider.

I've been using GrandCentral for a day now, I've taken a few calls using it, and it seems to work well. I had three people call me through GrandCentral; it worked successfully twice, and one caller got disconnected. The sound quality is good. If the quality keeps up, I'll start using GrandCentral as my primary phone number.

However, I can already see some limitations.

For starters, instead of the mumbo-jumbo about "groups," how about separate phone numbers you can give to different people? GrandCentral is trying to use rules and Caller ID to help us separate the roles we play in life -- friend, family member, business associate. But there's already a perfectly good way to separate those roles: Give out separate phone numbers to your people you know from your personal life vs. those for whom your relationship is primarily professional. That system has worked well for more than a century. It would be great if GrandCentral assigned a user at least two numbers.

Also, what happens if a lot of people already have your home, business, and cell numbers? You'll still get a lot of calls on those numbers. I suppose, eventually, die-hard GrandCentral users will get all their current phone numbers changed and have the old numbers forwarded to GrandCentral.

I'm already starting to leave messages for people asking them to "call my GrandCentral number," and then looking all smug when they're baffled. This allows me to enjoy the same feeling of superiority felt by the first people to have said, "Skype me."