With Gizmo5, not only can you use your PC to make or get phone calls on Linux, Windows, and Macintosh PCs. But unlike similar programs, such as Skype, Gizmo5 uses open standards like Session Initiation Protocol (SIP) and Jabber, which makes it interoperable with a variety of clients.
Previously known as the Gizmo Project, Gizmo5 is both the name of a Voice over Internet Protocol (VoIP) network (with its own servers and users, working over the Internet) and of a program that lets you communicate by using that network. Though it uses open standards, Gizmo5 doesn't qualify as open software itself. It uses several proprietary codecs, and the client code itself is closed source.
Gizmo5 offers several packages for Linux users, including RPM, .deb, binary tarball, and Click 'N Run versions. I used the RPM version, which worked fine under both openSUSE and Mandriva. Installation just requires running
sudo rpm -Uvh gizmo-project-126.96.36.199-1.i386.rpm. Make sure you already have the GIMP Toolkit (GTK+) 2.6, GConf2, libstdc++, and Advanced Linux Sound Architecture (ALSA) installed; the RPM package won't install those. After installation completes, you'll find Gizmo5 in the Internet section of your system menu; the program appears as Gizmo Project.
Unfortunately, Linux users don't get to use the latest versions of the software. The current available Linux version is 3.1.0, while Macintosh users can use 3.1.2 or try the 4.0 beta, and Windows users already have the 4.0 release. Even cell phone and Nokia Internet Tablet users can get more up-to-date versions.
The first time you start Gizmo, it asks you to create a user account. You have to provide a username, password, and email address (in case you forget your password). You can edit this information later from the Gizmo window. You may also pick an avatar for yourself, but Gizmo won't allow you to upload your own photograph, as several other programs do. As soon as you get an account, you get $0.10 credit, so you can perform test calls to any number. (If you call an USA number from the web, 10 cents buys you about five minutes at the current rates.) I experimented by calling home to Uruguay, and it worked perfectly. Gizmo5 installs itself in the system tray, so you can access it with just a click.
You can get some features of Gizmo5 for free, but you must open an account and pay for others, particularly those having to do with calls to mobile phones and landlines; rates vary depending on your country and what kind of number you call. The free features include calling other Gizmo5 users (with optional video to be included in version 4; Skype already offers it), call recording and voice mail, chatting (AIM, Windows Live Messenger, Yahoo! Messenger, Google Talk, Jabber, and more protocols are supported), and doing file transfers (but only with Jabber clients).
The paid features include calling or sending SMS messages to normal phones and getting a landline number so Caller ID shows your number. Note that many other programs don't provide Caller ID information. Many people automatically screen calls from unidentified numbers, but this won't happen if you get a land number. You can get a local number for about 30 different countries.
Gizmo is easy to use. To build up your contacts list, you will probably want to search for other people, in one of two ways. You can click on the looking glass icon and enter some text; Gizmo5 looks for users with that text in their first name, last name, city, state, or country. (Thus, a search for WASHINGTON brings up people with that last name, plus all users in Washington, DC, every user from the state of Washington, and others.) However, if you already know another person's name, you can simply click on the icon next to the looking glass (a head and a plus sign), and you'll be able to add that person to your account list quickly.
You can start one-on-one chats (by clicking the IM icon) or group chats (by clicking the icon next to the IM one). For the latter, you have to name your group session and add all the people you want to invite. For both kinds of chats, not everybody has to be in your account list; you can enter their usernames, and they will also be invited in.
For phone calls, right-clicking on an account name lets you start a Gizmo call (with other Gizmo5 users), a SIP call (with users on other SIP networks), or a mobile or landline call -- but for the latter, you will need enough credit; go to "Your account" on the Gizmo5 Web site and use your credit card or bank account to get it. You can also "dial" a number by clicking on a on-screen phone pad. For laughs, try out the silly special sound effects (such as "thunder," "tiger," or "boing") during a call when you think the other person isn't paying attention.
At a conference I attended, Ivar Jacobson of UML fame, who has several years' experience with telephony, pointed out that the telephone system was the largest successful system in the world. Each country has its own system, connections, and rules, but somehow you can call from any country to any other country, and talk to whomever you want.
The Web phone category isn't a single world right now. It's difficult to avoid comparing Gizmo5 to Skype, because they have many features in common. However, each application has its particular features, and depending on your interests, one might be better for your particular case. If you require free voicemail, chatting with Jabber users, having Caller ID, or calling other SIP networks, then Gizmo5 is your choice. From a more practical point of view, you should consider the calling rates for your country, or the cost of the special added services; depending on your needs, which program to use will be obvious.
However, the main point in using such a program is getting connected to other people. The success or failure of the companies that create these applications depends on how many people use the software. If the adoption rate of Gizmo5 keeps growing, the company might face off with Skype, and users are sure to benefit from that. For now, it seems that Skype has the advantage, but Gizmo5 merits attention. The program is solid, fast, and easy to use. Being able to connect to other networks is a useful function, and its reliance on open standards is a plus. For now, I'm keeping both.