you can transfer data between point A and point B on GSM networks too but the question is how much data? If you are planning to send 1x1 pixels monochrome videos then yes, the bandwidth is enough.
For bigger images and more colors, depending on the codec used, ONE MORE IMPORTANT thing you have to consider is the "BandWidth" available to you.... you will have some specific bandwidth needs but that is pure math so if you get down to it you can easily determined what is the highest quality video you can transfer.
Apparenlty Nokia and the operators have studied the issue and the conclusion was that they need to invest big money in more advanced devices and networks in order to support video telephony service. Most likely the reason was the same math ...