I am speculating here but it is my understanding tha a phone utility can not refuse service to residential customers, however the customer is not required to get the service. By mandatorying the wiring does make is possible and easier for the service after the fact rather due to change of mind or new owners and eliminates the installation expense. Of all the different codes, the NEC would be the most practical place to put it to ensure it happens since most phone utilities do no enter private residences. Just because it is in the NEC, it does not require an electrician to install it. Like I said, I am only speculating. I can be barking up a tree
