@calico55 Understand technology b4 commenting.
Airtel airheads, jio jokers and voda vampires can intercept your call. With the right equipment your call can be "picked" off the air.
MTNL monkeys(and your nosy neighbour)can listen to your call with a 500 re phone by tapping into the line. Does this mean in your words that phone calls were built to
communicate cheaply with their customers to inform about network downtime, invoicing and sending business cards
SMS are not free for the banks. They buy various "quality". Instant SMS (the EXPRESS sort you get on cash withdrawal b4 you walk out of the ATM/OTP) can cost say 5p but account credited SMS , the Janata version, which you get hours later costs maybe 1p.
Until a decade ago, USA had forbidden export of encryption technology (to certain countries including India). You could not pass on the latest version of PGP to your Indian friend for personal use.
Today WhatsApp and signal encryption is taken for granted but your basic phone does not have the processing power to handle it. Very few people/govts can intercept and decrypt these calls/msgs. Awesome security in the hands of
people.
Even normal messaging with cell no using Google chat (via net) uses tls encryption (though not end to end). You can enable your SMS app to use it.
In some countries even landlines work on the "net"... VoIP.
Jio fiber has introduced it in India so you can connect you POTS phone to the modem.