I (think) this is a (bad) pun.

'Yo' is both an informal means of saying 'hello' (much as in English speaking countries,) and　part of the Japanese (as opposed to the Chinese) word for 'four' (yon.)

'To' is not part of any greeting that I am aware of, but is the first letter of the Japanese (again, as opposed to the Chinese,) rendering of 'ten.'

The joke is now ruined. Carry on.