Nice question and an interesting example. Would renaming the columns "Telephone 1" and "Telephone 2" to "Home Phone" and "Mobile Phone" mean that the table was then in 1NF?
I would say no, because there can be other categories of phone, such as Business Phone. The phone number may not be the best example because it could be said that "I only want two phone numbers", in which case an argument can be made for having the columns in the main table. Not a great argument, as the single column in a seperate table still makes queries and searches easier, and if someone would ever come a long and decide they want to track three phone numbers, the seperate table is much easier to implement, as it is already so.