In the old days (!) telecommunications revenue worked roughly on 2 models. You either took a share of the revenue as a carrier or a share of the revenue as the terminator of a call. So making international calls, the cost was eaten up by a number of carriers, and if it was to a premium line the carriers would pay out to the terminator of the call (either one off charge or based off call duration). Right now, chances are you are still using your desktop email client or a Blackberry for reading and sending emails, so there is money being made in the client application or device. Nobody really pays for webmail, this is the domain of the advertiser.
Just as you got comfortable with this ... everything is changing. The web and broadband has meant that these days an increasing amount of communication is permformed online and in many cases through the browser. It is very interesting with the rise of social networking sites such as Facebook now being used as communication devices between people and groups of people how this affects previous models such as voice calls, email and SMS. These days email and SMS are routes for messaging, but the user may not be using their mobile phone or email client. Services like Twitter, Facebook and Skype have changed the traditional models of communication and throw into question how this can all be monetised. Unless you can monetise being a carrier or a terminator of the communcation, where is the money to be made? Blyk feel one way is to do all of this for free is to use an advertising model. It will be interesting to see if this model works on the long run, as it could be disruptive to traditional billing models for communcation.
With the level of communcations now being passed through social networks, person to person through the applications rather than email or text, what threat does this pose to mobile networks. To communicate with me, I can insist you need to be part of my friends list or some group ... with many tools available I have the power to decide where I receive messages from. If users could run an application on a mobile that hooks up with Facebook to do messaging, video and voice, why use the mobile network for anything other than data transfer? If I was in a mobile network right now, I would be paying close attention to this area as you wont be the ones in control of peoples communications and contact lists any longer.