PHONE CALLS
Telephone numbers consist of a three-digit prefix (area code) and the user's number. Manhattan's prefixes are 212, 646 and 917, while all other four districts in the city have 718, 347 and 917. Toll-free numbers are prefixed with 800, 888, 877, 866, 855 and 844. There are also some numbers called N11 codes that are easy to remember, are utilities that start with a number between two and nine and are followed by 11.
211 local community services and information;
311 non-emergency calls to the police and other government services;
411 telephone information;
511 traffic information;
611 generally used as a helpline service for problems with telephone lines;
711 Telecommunications Relay Service (TRS), used by deaf or hard of hearing and speech;
811 for information on whether excavations should be carried out in the ground (power lines, gas and water pipes, etc.);
911 emergency number (police, fire or ambulance).
USA -> USA
Public telephones work with coins, in case of long or long distance calls the operator may interrupt the call to ask to insert more coins. For long-distance calls, the number 1 is always added before the area code (e.g. 1-310-7182778) and if the number 1 is replaced by 0, an operator answers.
Sometimes in the United States telephone numbers are indicated by letters, in this case just look at the keyboard of the phone to find the corresponding number (eg. 1-(800) CALL-ATT).
USA -> ABROAD
To call a phone in another country from USA, dial 011, and then the code for the country you are calling, the area or city code, and the phone number.
Mobile Phone
Telephone rates, when calling from your national mobile, depend on the operator used and the agreements made with the American companies. Before you leave, we recommend that you check with your operator for rates and promotions for the United States.
You can also opt for the purchase of an American Sim Card, avoiding the tariffs with contract and buying in cash a prepaid rate. In this case you can check if your phone will work with an American sim card on the site
Will My Phone Work.
Internet
Using an app like Skype or WhatsApp from your smartphone or computer is probably the cheapest system. Of course, it's better not to use data roaming, always very expensive, but to use one of the many free WiFi hotspots.
The top five American telephone operators are:
Verizon Wireless
AT&T Mobility
T-Mobile US
Sprint Corporation
U.S. Cellular
References
International Calling Check List (Federal Communications Commission)
What Is a Toll Free Number and How Does it Work? (Federal Communications Commission)
List of ITU-T Recommendation E.164 assigned country codes
How to Make International Calls from the USA (wikiHow)
INFORMATION
ITA