What does "Pre-notice of a domestic smartphone number" mean?

It's an option available for domestic smart phone rental services. 

 

We provide the phone number that you are renting out 2 days before the pick-up date. With this option, you can know your number earlier than 2 days. 

 

If there is no need then please proceed with your order form without this option. If you wish to know your number 3 days prior or earlier then please select this option.
※Please note that this option will incur charges.