I agree that there's a problem with the "Radio?" line, and I picked it up on first viewing. I think I'm probably in general agreement with
gottacook here, although my explanation for why it's a problem differs somewhat.
The problem is that the conceit that radio is too primitive creates a disconnect with the audience. It's just another brick in the wall laid by
Star Trek taking itself too seriously for its own good.
However, I don't consider it as much a problem in the script as it is in the delivery. Instead of conveying that he's not heard of radio in ages, as by "Radio???" (don't forget that Spock has just off-loaded some technobabble, via "A simple binary code transmitted by carrier-wave signal. Radio."), the delivery should denote surprise, if not amusement, because Kirk knows good and well what radio is, as in "Radio?!?"
A follow-up line wouldn't have hurt either, explaining why it's a surprise, but there's yet another problem. V'Ger's shift to a primitive form of communication could have been reasonably interpreted (based on what they knew at the time) as evidence that it is aware that its previous communication was problematic, and that it believed that Earth might have the same difficulty receiving and responding as the
Enterprise initially did. In other words, it might have been taken as evidence that V'Ger was finally starting to appreciate carbon units.
So, a smart follow-up line would be in the vein of:
"Radio?!? First they signal in ways that we almost cannot comprehend, and now they use methods that we advanced beyond centuries ago. What does it mean? Are they finally trying to talk down to our level?"
Besides all that, the level of surprise in the use of radio conveyed in the film doesn't even mesh with other dialog of TMP itself. If you dissect the technobabbly
"photic sonar" scanning technology, you find
RAdio Detection And Ranging. "Photic sonar" is even more eye-rolling than Kirk's surprise at the use of radio, given that
sonar stands for
SOund Navigation And Ranging. Comparing light to sound just to be cute is more advanced? Really? Why they had to say something that made the writers sound ignorant instead of just saying
radar is beyond me.