You say that, but phone phreaking was possible because of in-band signaling. People back in the day had much the same tradeoffs we did; by necessity, they just came down on the side of less security / less portability / less reusability.
NASA would not have used this technique of they had today's signal proccessing/bandwidth/resources. They used these clever tricks because that was the only option.
These clever tricks have major downsides. They are more fragile and easier to get wrong. Just like code today, the most clever code is often the least maintainable.
