Gallons makes sense. I could wrap my head around the 15 gallons I used to put in my car's tank. What I wouldn't want to wrap my head around is thinking about putting ~56,781 cubic centimeters of gas in my tank.
If you require someone to perform multiplication beyond 10^1 scale to estimate costs, it becomes easier for telcos to overcharge users. You and I probably have no issues with multiplication in our head on the order of 10^2 up to 10^6, but for most users, that scale is mentally taxing.
Compare:
0.02 cents per sms message
$20 per 1000 sms messages
Plus, prices are "stickier" at 0.02/message than 20.00/1000 messages, since it's easier for two telcos to start discounting their price relative to one another with the latter, like $15/1000 vs $20/1000. The equivalent to such a discount under the per message pricing schema is to charge fractions of a cent. i.e. 0.015/message vs. 0.020/message. The only place in society where we really see fractional cent pricing in daily life is with gallons of gas, and even there the burden for the end-user is high enough that the gas stations all get away with leaving that fractional amount at nine tenths of a penny almost all the time.
If you require someone to perform multiplication beyond 10^1 scale to estimate costs, it becomes easier for telcos to overcharge users. You and I probably have no issues with multiplication in our head on the order of 10^2 up to 10^6, but for most users, that scale is mentally taxing.
Compare:
0.02 cents per sms message $20 per 1000 sms messages
Plus, prices are "stickier" at 0.02/message than 20.00/1000 messages, since it's easier for two telcos to start discounting their price relative to one another with the latter, like $15/1000 vs $20/1000. The equivalent to such a discount under the per message pricing schema is to charge fractions of a cent. i.e. 0.015/message vs. 0.020/message. The only place in society where we really see fractional cent pricing in daily life is with gallons of gas, and even there the burden for the end-user is high enough that the gas stations all get away with leaving that fractional amount at nine tenths of a penny almost all the time.