In 1990, I invented Call Back, a means of routing telephone calls through the United States who at the time was the only country who had liberalized its telecom sector and its long distance rates where a third of those overseas.

Call Back was what drove Viatel during its first years of existence. Viatel later evolved to become the company to build a fiber optic network throughout Europe in anticipation of the liberalization of telecommunications. In 1999, when I sold my shares in Viatel, the company was worth over a billion dollars. After selling Viatel I came to the conclusing that tariffication per minute was about to die. My next companies, Jazztel and were oriented more towards the Internet than telephones. But it seems that my call for the death of the minute in telecoms came too early. We are in 2007 and still the most profitable sector of telecommunications, companies like Movistar and Vodafone consists in ripping their customers off charging per minute, rather than flat rates as DSL operators do. And that is why numerous companies continue to arise with the desire to exploit the per minute business of VolP services for cell phones.

Many start ups offer this service. I’ve prepared a short summary of the available options. Personally, I’m happy with fring. Fring is great if you have certain Nokia models. I use the N80 and get to combine my Nokia contacts with Skype, IM and Google Talk and talk for free to many of these or through Skype which is cool cause Skype is not on Symbian yet. Other than having Fring on my Nokia, I also have one of the phones that Skype sells to FON. The Skype phone’s weakness is that FON is still not as widely spread as it will become but other than that it works great and it costs 70% less than the Nokia.

What follows is my research on what else is there in the market.


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In the first place, we can differentiate between those services that offer direct calls (fring, Truphone, Skype Mobile, Gizmo Project and those that use callback, requiring you to first connect to a server (Nimbuzz, Jajah, and Talkster). With Fring, for example, all you have to do is enter the number that you want to call and hit send. Talkster, on the other hand, only completes your call once a connection to the system has been established. iSkoot is a particular case: it’s the only service that works using the standard H.323, connecting to users through a VolP-enabled PC.

In general, iSkoot and this first group of options require the user to install free software into his or her cell phone. The second group, however, functions differently. Nimbuzz and Talkster can make calls without having a special program installed in the phone. Jajah, on the other hand, requires you to connect to its portal: you enter the number there and Jajah completes the call.

Also important is the location and equipment necessary for the use of each service. Fring, Truphone and Skype Mobile can be used in any Wi-Fi area. fring can be installed in all models of Symbian 8 and 9, Truphone uses Nokia’s E Series and Skype Mobile the “Skype Wi-Fi Phone”, Nokia N800 and WM. Within the second group (which also includes iSkoot) none of the services are compatible with Wi-Fi. Nimbuzz works in places with available local access numbers, and connects to the network through any WAP or J2ME device. Jajah and Talkster use WAP telephones, and iSkoot uses the Nokia N73 and Sony W950 models.

The services can also be distinguished by their interoperability with VolP services for PCs. Fring can operate with many platforms. Truphone operates using GTalk, while Skype Mobile and iSkoot only use Skype. Within the second group, Nimbuzz and Talkster operate with Gtalk and MSN, while Jajah uses neither. Fring, Nimbuzz, Skype Mobile and iSkoot also have additional chat services and presence-control technologies. Talkster offers the latter. Truphone and Jajah lack both.

Another comparison point is the price of the devices and their network requirements. Fring, Jajah, Talkster and iSkoot need 2.5G (GRPS) or 3G plans to complement WiFi. Nimbuzz works with 2.5G and the rest of them have no special requirements. Calls between users of the same service and services that work in conjunction are generally free, except in certain cases with Jajah and Talkster (the cases are variable) as well as iSkoot (for which the annual cost is about 10 US dollars). On the other hand, while neither fring, Skype, nor Nimbuzz consume GSM minutes, the rest of the services do. For calls on the public network (PSTN), fring, Skype Mobile and iSkoot (although not all versions) use SkypeOut. Truphone, Jajah and Talkster also allow these types of calls, while Nimbuzz only works between cell phones and from cell phones to PCs.

I would like to emphasize that Rebtel is the company of my friend Hjalmar Windblad. Rebtel is perfect for international calls and for people who do not want to buy a new phone as it works on all mobile phones. For example, if you live in Spain but your parents are in Argentina (my case), you go to Rebtel, obtain a number in Buenos Aires and authorize the number to ring in your cell phone or landline in Spain. Then, every time that your parents want to call you they dial your number in Buenos Aires, a local number, and your phone in Spain will ring. And you will only have to pay the cost of a local call made in Spain. The downside of Rebtel is having to change your number, but the upside is that people prefer to dial a number in their own city and not an international number.

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John on February 27, 2007  · 

We’ve been using VoiceStick here for demos of our hotspot login software on the Linksys WIP300 (a Wi-Fi only SIP phone). VoiceStick offers flat rate calling plans, or a per-minute option with no monthly fees. They also give you a local number in some parts of the US or UK for free, so people can call you easily from a regular phone. Services like Gizmo and Skype have call in numbers, but you have to pay extra for them.

It works well too. Really fast registration when you switch the phone on, and clear calls. They have a very cool feature that bridges a cell phone or landline onto your account so you can make international calls from your cell phone using VoIP instead of the cellular company. Check them out.

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PanMan on February 28, 2007  · 

I have looked a lot at options like these, and always found that they weren’t attractive for me. If I did a lot of international calls, or even calls to fixed lines, I could use one. But with my profile of mostly calls to mobile phones within my own country, they aren’t cheaper.

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Joachim Simon on March 1, 2007  · 

Martin, thanks for the great overview! Just one addition for Germans: I am living in Germany where there is a new service popping up and hyped in the media as well. It is called cellity (see ) and works as a least cost router by connecting you anywhere via their server. You pay the fixed line cost to their server and an additional fee for their part of the connection.
It works via a software you have to install on your mobile device and (negative point) this only works with newer cell phones.For those who have a Base Flatrate where landline is included anyway it seems to be a good option.

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Martin Smink - Nimbuzz on March 1, 2007  · 

Hi, thanks for the analysis.

However, the sheet uploaded is outdated. Please goto for an up-to-date comparison of the various players’ functionalities.

Specific about Nimbuzz: Nimbuzz is NOT a call back service. Calling with Nimbuzz is all about calling in to a local accesspoint via GSM to reach international contacts on the big IM/VoIP and social communities. International calls at local cost. Because there is no call back, Nimbuzz does not require credits which is very convenient for its users avoiding the use of creditcard tx on the internet.

GPRS = 2G as far as I know. Nimbuzz does use the 2G for sinalling and IM but calls take place via GSM with local access in 35 countries.


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Tim C on March 5, 2007  · 

Hi Martin,

I wonder can I add a bit on barablu……

We combine the best attributes of the above and more in one package called barablu.

We are also integrated with Skype and Google Talk, and have full online presence. Our instant messaging service works over GPRS. We also have our own barablu out service which offers calls to landlines and mobiles at cheaper rates than Skype.

barablu works on over 47 different handsets including Nokia N and E Series, and we are very proud of this. We are bring out new phones every day.

Full list of handsets are on


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