What's the difference between sending text messages and making phone calls in terms of signal transmission?

Exactly the same, it's all by modulating the carrier, then converting the signal into binary, loading it on the carrier, transmitting it, receiving it by the base station and transmitting it to a farther place through the line.

But the average Chinese character is about 2 bytes, and the pronunciation is about 8000 bytes per second. So the semaphore is different, but the short message is actually sent instantly, just need to establish a link before launching.

So, it's all the same, all using electromagnetic waves.