lts,

that telephone one you're on about wsn't originally a commonplace gesture. its come to mainstream use from bsl & makaton. these are signing systems. bsl used by deaf people, & makaton by people with other communication difficulties.

i did a makaton refresher course some time back & it was noticed by other students that the sign for plane [airplane] was nearly the same as the phone one except you mime the plane flying through the air.

this came to be interpreted also as 'flying telephone!'