Cellular / Wireless
Paper cups with string stretched between them
The "Heavenly voice ringing down from the sky" technique
Results (436 votes), past polls
By rote learning.
Via Genetic memory.
It's provided by my firmware.
I just remember them.
Thirty days hath September
My computer gets it right, usually.
I just ask someone else.
Someone punches me on the first of the month.
Results (239 votes),