The last loop
Having a telephone number is one thing. Being able to make phone calls is another thing. By ordering a telephone number, the phone company opens a billing ID and a link to the telephone box on the side of your house. They do not provide the connection from this box to the wiring in your home. This is something you either have to do yourself, or order the phone company to do (at extra cost).
If you have a new house, all the wiring will probably be there. If your house is old and not used for a while, it may be required to reconnect the inside wiring to the phone box. If you are familiar with telephones you are probably able to figure it out yourself. The customer is allowed to open one side of the outside phone box, where it has several phone extensions. You have to connect the inside wiring to a line that works.
In our case, we had to find out ourselves which of the lines in the box next to the house was ours, and in fact we found two lines that worked. By calling from one line to the other we could determine the number that was ours. By calling from the other line to a phone that had calling number display we determined the other number. With that number we called Bell Atlantic and asked if this was a free extra line or so. They did not agree with that and promised to send an engineer. In the mean time, we received several calls on our 'foreign' line, and fell into two-party conversations about catering and cleaning services. The other line on the outside of our house apparently was in use by another household!
The engineer from Bell Atlantic mumbled something about 'touristic connections' and that the extra line on our house should not have been there. So she got her climbing gear on, climbed a telephone pole near our house (8 meters high), and connected the line in another way. Lesson: your phone line may be crossing one, or more, houses before it heads off for the local exchange. Overhead wiring for telephone, cable tv, and electricity is common in the USA, with all the risks of snow, wind, or lightning cutting the connection.