Talkster (free.talkster.com) is a VOIP based service that lets you make "free" ad supported phone calls between 22 countries (North America, most of Europe, plus Hong Kong and Israel) using any phone - mobile or landline. The ads are about 10 seconds long and are heard by both parties.
Talkster doesn't charge anything for the service but the calls aren't really completely free. You're making a mobile or landline call to a local Talkster access point. If you are using free night and weekend minutes or an unlimited landline then Talkster calls really are free. But even if you have to pay for the local call, Talkster will be much cheaper than a normal international call.
Using Talkster is a bit complicated. Say you want to call your friend in Spain. You go to the Talkster mobile or PC web site and enter your number and the number you want to call, Talkster texts you a new permanent local number that connects with your friend and also texts your friend a local number that connects to you. You call your friend's Talkster number and are connected. Now here's were it gets tricky. The initial connection disconnects in about 10 seconds - just enough time to tell your friend to call you back on the number that Talkster SMS'ed to her and which also appears in her caller ID as the number you are calling from. You stay on the line and Talkster completes the connection after you have both listened to a 10 second ad. Obviously not something you can use for business calls or booking hotels but completely practical for calling friends and family members. Pluses for Talkster is that it doesn't require 3G or WiFi as the local loop is provided by your mobile or landline phone company and you don't need to register or install anything to use the service
Talkster competes with Jajah and Rebtel which also offer cheap and limited free international calls from mobiles and also require you to initiate the call on the mobile web. The others are easier to use, cover more countries and are more business call friendly (no ads and generally no callbacks) but Talkster has one big advantage - unlimited free calls.
I have my doubts about the long term viability of Talkster's business model. Can they sign up enough advertisers at high enough rates to cover the cost of access points and bandwidth? Their target market, personal calls between friends and family members, is one were calls tend to be long. Can a single ten second ad cover the cost of a two hour call?
Update: Thanks to Chai340 for pointing this out, Rebtel is now offering unlimited free calls without ads using a callback scheme similar to Talkster. Nice, but obviously not economically substainable, enjoy it while you can!
Talkster (xhtml-mp) Content: Usability: