Compared to videocom radios, subspace radios are expensive and power hungry. The radio itself costs 20,000 Cr. It requires a Type I Parabattery to run (or needs to be attached to a larger power source) and uses 100 SEU to send a single message. And with a mass of 100 kg, it is too bulky to be carried and require a relatively fixed installations either on a planetary surface, station, or ship. It could be mounted on the back of a ground vehicle, but beyond a few military applications, there isn't much point, as the increased complexity of operation would counteract any advantage the mobility gained you.