" The choice of 7 digit number was made because that's the ideal number for humans to remember."
Those people shouldn't have telephones.
I probably know 20 phone #s that I use, my SS#, bank account #s, etc. and never write any of them down.
I routinely dial huge strings of digits to reach people. The company card access number is 11 digits to the prompt, 14 digits for my "pin", then 11 digits to call a number in the United States. It's particularly irritating when I call my colleague at his office in Mclean, VA and discover he's not there. I get to do the whole 36 digit dance again for his cell phone.
I would love to automate this nonsense, but the carrier has an indeterminate period between dialing the access number and the time it will start accepting digits. If you don't wait out the double beep and voice announcement, you may have to dial the whole 11 digit access sequence again. Very annoying.