Jajah
Jajah describes itself as "Skype without the headset." It's a VoIP phone service, but you don't need any special equipment to use it -- it completes its calls on standard telephones, either landline or mobile.

Jajah's lets you enter the number you want to call from a browser; the service will ring your phone and the phone you're calling. (Click image to enlarge.)

To make a Jajah call you go to www.jajah.com and enter two numbers: the phone you're calling from, and the phone you're calling to. Your phone will ring, and you'll be connected to your call. Jajah is a European-based service, and it accepts Visa, Mastercard, American Express, JBC and Diners Club. You can put in as little as $5 to start.

There is an incentive for you to get people you call regularly to sign up for Jajah, as well -- Jajah connects registered users for free. There are some restrictions -- calls to or from mobile phones are free in some countries and charged in others, for example, and no free service is available in some parts of the world. Call quality can be variable -- I experienced some strange clipping effects in some trial calls.

Rates for calling unregistered numbers are similar to other VoIP services: for domestic numbers in the United States it's 2.8 cents a minute; overseas rates go higher. And the difference between landline and mobile is significant, too -- a call from the United States to France, for example, costs 3.1 cents a minute if the connected phone is a landline, 17.6 cents if it's a cell phone. (That call to Wallis and Futuna is 82.5 cents a minute on Jajah.)

Jajah is developing features that take advantage of the computing power behind VoIP calling. The service offers conference calling, scheduled calling that works for both personal reminders and conference calls, and SMS from your PC to mobile phones. It is currently beta-testing "dynamic buttons," similar to GrandCentral's click-to-call feature that lets visitors to your Web site phone or text you without revealing any of your personal data.

Jajah looks like it has legs, if its investors are any indication. Earlier this year it raised $20 million from the likes of Intel and T-Mobile. As mobile phone companies stop resisting the inevitability of WiFi access and VoIP over their services, Jajah looks well positioned to become a business partner of the big providers.

Talkster
Talkster works like Jajah for phone-to-phone calls, but with a slightly different marketing twist -- instead of free calls between registered users, its gimmick is free calls to voice-enabled instant-messaging services. So you can set up a call from your Web-enabled mobile phone to somebody on your buddy list on MSN or Google Talk (and Gizmo Project addresses, as well).

Talkster is designed to be used from Web-enabled mobile phones, so the user interface on the mobile site is minimal. (Click image to enlarge.)

If you're a regular user of IM-based voice services from your PC, Talkster extends your access to buddy lists to your mobile phone. And if you're calling phone numbers in other countries, Talkster allows you to avoid any restrictions on international calling that your cell phone account might impose.

Talkster pushes the VoIP envelope in the direction of presence, the ability to see whether the person you want to communicate with is online, and how. Once you've set up your voice IM contacts in Talkster, you can see your buddies' presence information from your mobile phone's browser. (Talkster does this without installing any software on your phone, either.)

Talkster's rates for calls connected to the public telephone network are similar to Jajah's -- that call to France will cost you 2 cents a minute if you're connecting to a landline phone, 23 cents if it's a mobile. (The ever-popular Wallis and Futuna: 81 cents a minute.) Talkster accepts Visa, MasterCard, American Express and Discover through InternetSecure.

Talkster's technology has an immediate benefit -- it lets you pick the least expensive way to reach your contacts -- and it's got long-term potential as well, because voice communications are moving away from reliance on the 10-digit telephone number and over to Web 2.0 addressing schemes, such as IM handles that can be resolved to IP addresses. Talkster is positioning itself for the future.