fx, FIOS service has historically not been available to Multi-Dwelling Units (MDUs) because they hadn't figured out how exactly they want to serve such properties. My understanding is that they now have a special MDU ONT in some markets that they can use to serve MDUs. However, some cooperation from the landlord is going to be required, and not all landlords are forward thinking.
Also, if your MDU has your phone service provided through someone not the phone company (some landlords contract with PBX kinds of people in order to get a cut of your phone revenues), then you're probably SOL.