The 1/2 second delay isn't bad when you start thinking about everything going on between those two phones.
If they have the same service, the phone itself encodes your voice, sends it to the tower who sends it to a processing hub that sends the data to a distribution hub who sends it to the receiving tower processing hub and out to the tower(if they are on the same tower this still happens and most of the time has to be sent to another distribution hub) and then sends it to the phone where the audio is decoded.
If they are on a different carrier then the signal goes even further. With everything that happens behind the scenes, it's pretty incredible how fast you are able to hear the other person talk! And on top of all of that a single tower can be taking care of 20+ calls easily and the distribution centers handle thousands of calls at one time.
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