Besides the whole fire thing, which is a serious problem for the metallurgy necessary to make radio, to have any chance of it they'd need to get fingers instead of the optimal swimming flippers they have now. They'll never do that as long as they're aquatic. If millions of years of evolution has them climb out of the water and become land animals again then there might be a glimmer of hope for them, but then they'd no longer be recognizable as dolphins. As it stands now, field mice have a more direct path towards becoming radio makers than dolphins do.

Living underwater puts a dampener (didn't intend this atrocious pun, sry about that) on any technology that depends on fire. So smelting ores seems out of the question, and of course radios are made out of lots of pieces of metal.

I can't think of any plausible ways a water-bound species would be able to harness and use electricity either