I try to restrain myself from calling any new tech product or service a killer. But Google just announced that it’s integrating Google Voice into Gmail, turning its e-mail service into a fully Web-based Voice-over-IP system that lets you talk to people with landlines and cell phones all over the world. And…well, it looks like it could be an awfully compelling Skype alternative. Especially since calls to cell phones and landlines in the U.S. and Canada that you’d pay for with Skype are free.

The integration adds a cool new feature to Gmail, but as a long-time Google Voice addict, I’m even more excited about what it does for that service. Now those of us with Google Voice numbers can use it in a new way, and without burning through mobile phone minutes.

A few details on the service, which rolls out today to U.S. Gmail users (Google Apps Gmail accounts aren’t yet supported, alas):

–Google says it has no plans to charge for calls within the U.S. and Canada; ones to dozens of other countries are two cents a minute;

–You can both make outgoing calls to landlines and receive incoming ones; both types are integrated with your Gmail address book;

–As before, Google Voice can ring multiple phones at once in order to reach you wherever you are–it’s just that one of the “phones” it can now ring (once you’ve enabled the option) is Gmail;

–You don’t need a Google Voice phone number to make calls;

–You can switch calls back and forth between the Gmail interface and cell phones or landlines;

–Google is touting the audio quality–and says that it’s great even if you just use your computer’s built-in microphone and speakers rather than a headset;

–The feature uses technology from both the Google Talk voice chat feature and Gizmo5, a VoIP company which Google bought last year;

–Google doesn’t have anything to say about the interesting idea of integrating Google Voice into the version of Gmail for mobile phones (you can already use Google Voice on your phone, but it’s making and receiving standard calls, not free VoIP ones);

–It also isn’t saying anything about a Google Voice app for PCs or Macs (which seems like it might be especially handy for incoming calls–right now, you need to have Gmail open and switch to it to answer a call);

–Google plans to install red Google Voice phone booths–yes, phone booths–at airports and college campuses to let folks try the service.

The interface for all this looks very straightforward: The existing Google Chat toolbar in Gmail now lets you place calls, and there are a dialpad and an incoming call alert that pop up in Gmail’s lower right-hand corner. A few fuzzy images from Google’s presentation:

And here’s Mashable’s Ben Parr trying out a Google Voice phone booth:

More thoughts once I’ve had a chance to try the service myself. If you’ve got access, give it a try and let us know what you think.

This story, "Google Voice and Gmail Mix to Make U.S. Calls Free" was originally published by Technologizer .