They can be up to 15 digits long: so as long as the format change that goes from length x to length x+1 doesn't break that limit, then no changes to code or equipment needs to be done. The routing just needs to be tweaked so that when a number is read the signal is sent to the correct destination.
This is different from IPv4 where the digit length needed to be changed. It would be like if telephones went from 15 digits to 20+ digits: all the telephone gear would have to be changed to deal with the larger numbers.
Phone number lengths are defined by ITU E.164:
* https://en.wikipedia.org/wiki/E.164
They can be up to 15 digits long: so as long as the format change that goes from length x to length x+1 doesn't break that limit, then no changes to code or equipment needs to be done. The routing just needs to be tweaked so that when a number is read the signal is sent to the correct destination.
This is different from IPv4 where the digit length needed to be changed. It would be like if telephones went from 15 digits to 20+ digits: all the telephone gear would have to be changed to deal with the larger numbers.