Prisoner of Fire, it's by the now largely forgotten British science fiction author Edmund Cooper. Back in the 70s he was quite popular and wrote a whole string of SF novels, but, to be honest, I can see why he's largely forgotten. The writing style seems from a different era, mannered and dated.
However, Cooper's ideas are still interesting. The topic of the book is the common enough SF trope of paranormals - it features a number of children with mental abilities, able to read minds, to block other telepaths, or to kill remotely. The reason it's interesting is that Cooper examines what such a capability would mean for governments, both in terms of protecting themselves and espionage, and how it could lead to an 'end justifies the means' attitude to the young telepaths as weapons.
That's not why I bring the book up now, though, so forgive the long introduction. Prisoner of Fire, written in the 1970s and set in the 1990s, wildly over-predicts technological advances. This was a common problem in the 60s and 70s. Things had moved on so much since the Second World War that it was assumed changes would be even more dramatic in the next 20-30 years. (Think how much 2001, A Space Odyssey from the late 60s overshoots what 2001 was like.) So Cooper merrily deployed hover cars, tri-vees and v-phones.
As I point out in Ten Billion Tomorrows, the problem with hover cars and tri-vees (in case you hadn't guessed, TVs that project a 3D image into empty space, a bit like the Princess Leia bit in the first Star Wars), the problem is that the authors weren't really thinking through the technological advances required. We just don't know how to practically make a car that floats or to project a hologram onto thin air. However, the v-phone is a more interesting one because we effectively have the technology but rarely use it.
I assume v-phones were video phones (it's never explicitly explained). These days, pretty well any smartphone or internet-connected computer is, in effect, a video phone. Using Skype or FaceTime, we can make video calls. And occasionally, for example, when family is on the other side of the world, they are very effective. But for 99% of our calling we don't use them. Because they feel strangely unnatural. The assumption has always been (video phones have been talked about since Edison and Tesla's day) that we would get the same benefits from a video call as a face-to-face conversation. And this can work with a sophisticated video conferencing setup. But for a chat on the phone it's a disaster.
There seem to be a number of reasons for this. One is that a smartphone is too up close and personal. It doesn't seem quite as bad on a computer where you can sit well back from the camera, because the view will take in a fair amount of the room. But on a smartphone video call, the other person's face pretty much fills the screen. To have an actual conversation with a person whose face fills your vision to that extent you would need to be around 10cm away from their face - a position that we just don't have conversations in, even with intimates, let alone strangers.
Another difficulty is focus. Although good listeners spend a lot of time looking at the person they are talking to, they also look away a fair amount, if only for fractions of a second. A solid focus on someone's face is intimidating. But in a video call, the other person is pretty much constantly looking straight at you.
Finally (I'm sure there are more issues, but these are the three that occurred to me), we don't always want the exposure that comes with being seen. A telephone is useful for many conversations precisely because we don't want to give too much away, whether it's because we're answering the phone in our pyjamas, because the room is a mess, or because it makes it easier to lie.
So poor old Edmund failed on all three, but the v-phones were arguably the most interesting fail because it's technology we can use, yet mostly choose not to.