Was talking to my friend (native Chinese) the other day and when she read out a phone number she said "yao" for all the "ones" in the phone number. However, as far as I remember, for all other cases ...
I always knew, from my studies of Japanese, that the number two is 二 (èr). I am not sure about the actual etymology, but looking at the character, it's understandable why it represents the number "2". ...