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In the North American Numbering Plan (NANP), toll-free telephone numbers have the area code prefix 800, 833, 844, 855, 866, 877, or 888. Additionally, area codes 822, 880 through 887, and 889 are reserved for toll-free use in the future. 811 is excluded because it is a special dialing code in the group NXX for various other purposes.
Calls to the toll-free numbers are charged to the receiving party, and are free to the caller if dialed from land-line telephones, but may incur mobile airtime charges for cellular service.
Most carriers in the United States and in all of Canada use flat-rate billing for local calls, which incur no per-call cost to residential subscribers. Long-distance calls have higher prices. As regulators in North America had long allowed long-distance calling to be priced artificially high in return for artificially low rates for local service, subscribers tended to make toll calls rarely and to keep them deliberately brief.
Some businesses, targeting to sell products to buyers outside the local calling area, were willing to accept collect calls or ordered a special service from the Local Exchange Company, such as Zenith or Commerce numbers, where the called party paid the cost of receiving telephone calls. Initially, all of these calls had to be completed by a telephone operator.
The first automated toll-free telephone numbers were assigned with area code 800, created as inbound Wide Area Telephone Service (InWATS) in 1966 (U.S. intrastate) and 1967 (interstate). These terminated on special fixed-rate trunks which would accept calls from a specified calling area with either no limit or a specific maximum number of hours per month. The billing of calls was not itemized and the expensive fixed-rate line was only within financial reach of large corporations and government agencies. Typically, a service provider offered a variety of zones, each costing more than the smaller ones, but adding progressively larger areas from which calls would be accepted for a customer.
In the early 1980s, Bell Labs received a patent for what became AT&T's "Advanced 800 Service", a computer-controlled system where any toll-free number could point to any destination number, such as to a small business local number instead of a special InWATS line, and an itemized bill generated only for the calls the business actually received. By breaking the link between the number's exchange prefix and geographic location, this system opened opportunities for vanity number advertising – an advantage in media like commercial radio where numbers need to be memorable.
Prior to the toll-free long distance market was opened to competition after 1986, a customer may have had a multi-carrier toll free number assigned by the Local Exchange Company for intrastate callers and an order placed with a long distance company for interstate callers. A RespOrg system was implemented in 1993 to provide toll-free number portability between rival carriers using the SMS/800 database. Open competition also brought an end to the pattern of long distance subsidizing local service, bringing per-minute charges down to levels where any business could afford to take orders using an 800-number.
Originally, 800 service in the US and 800 service in Canada were isolated from each other, but in 1984, an agreement between carriers in the two countries allowed the numbers in each country to be accessible to the other. Providers of 800 service were able to add zones to cover the expanded areas able to be offered. However, toll free numbers in the format of 800-NX2-XXXX may have been working for different customers in the US and Canada and not able to be extended beyond that country's border until the corresponding number became spare and assignable.
NANP（全米電話番号ネットワーク）におけるフリーダイヤル番号は、連邦規則集（CFR）第52部第101条によって規制されています。SMS/800データベースでは、RespOrg（責任組織）が番号を割り当てます。このデータベースは、連邦通信委員会（FCC）が民間企業に委託している番号管理サービスセンター（NASC）によって管理されています。
SMS/800データベースとRespOrg構造は、米国とカナダで使用されています。一部の特定の交換局は予約済み、またはSMS/800プールから番号を取得しない特定の北米番号計画国に割り当てられています。
最初のフリーダイヤル市外局番である800は、780万件の番号が枯渇するまで30年以上運用されましたが、新しいフリーダイヤル市外局番は、VoIP、ポケットベル、住宅、中小企業での利用の拡大、個々の広告に対する反応追跡（各クライアントの広告ごとに異なるフリーダイヤル番号が割り当てられる）、または販売、リース、共有利用などにより、ますます速いペースで枯渇しています。
これらのフリーダイヤル番号はNANP内のどの電話からでもかけることができますが、所有者（場合によってはプロバイダー）が使用制限を設けることがあります。特定の地域からの通話のみを受け付ける場合もあります。公衆電話からはかけられない番号もあります。米国では、FCCの規定により、公衆電話からの通話にはフリーダイヤル番号の所有者に追加料金が発生します。フリーダイヤル番号はNANP外からは利用できませんが、多くの国際電話サービスはダイヤルインポータルを介して米国経由で通話をルーティングします。
米国では、Sprint、AT&T Inc.、Verizonなどの交換局キャリア（IXC）と、 VerizonやAT&Tなどの地域交換局キャリア（LEC）の両方がフリーダイヤルサービスを提供しています。[ 2 ] [ 3 ]フリーダイヤル番号の処理方法は、国内通話か交換局通話かによって異なります。ほとんどの国は交換局と呼ばれる地域に分割されており、各交換局内では、地域の電話会社がすべての電話サービスを扱っています。[ 4 ]地域内に留まる交換局内通話は、個々の地域の電話会社によって管理されます。米国のLATA境界を越える通話、またはある国で発信され別の国で着信する通話は、交換局通話と呼ばれます。
フリーダイヤル番号の形式は、地理的な番号である世帯番号とは対照的に、非地理的番号と呼ばれます。（携帯電話とVoIPの登場以来、世帯は米国内のどの市外局番でも使用できますが、その市外局番からの通話は市内通話とみなされるという意味では、依然として地理的な番号と言えます。ただし、受信者は物理的にはどこにいても構いません。）後者の場合、市外局番から発信者のおおよその位置（例えば、ニューヨークやロンドン）を特定することが可能です。一方、フリーダイヤル番号は、物理的には世界中のどこにでも存在し得るのです。
フリーダイヤル番号にダイヤルすると、電話会社はネットワークに組み込まれた高度なネットワーク機能を利用して、実際の物理的な接続先を特定します。最も単純なケースでは、フリーダイヤル番号は通常の市外局番付きの番号に変換され、電話交換機によって通常の方法でルーティングされます。より複雑なケースでは、時間帯ルーティングなどの特別なルーティングルールが適用される場合もあります。
フリーダイヤル番号は通常、国ごとに固有です。カナダの番号は例外で、他の北米番号計画の国々と同じSMS/800プールから割り当てられます。+800ユニバーサル国際フリーダイヤル番号も例外で、複数の国コードから利用できます。ローカル交換キャリア/インターエクスチェンジキャリア、州内/州間、LATA構造といった恣意的な区別は、米国独自の規制上の仕組みであり、カナダや他の国には直接的な類似例はありません。
The IXCs generally handle traffic crossing local access and transport area (LATA) boundaries. A LATA is a geographical area within the U.S. that delineates boundaries of the LEC.[5] LECs can provide local transport within LATAs. When a customer decides to use toll-free service, they assign a Responsible Organization (RespOrg) to own and maintain that number. The RespOrg can be either the IXC that is going to deliver the majority of the toll-free services or an independent RespOrg.[6]
When a toll-free number is dialed, each digit is analyzed and processed by the LEC. The toll-free call is identified as such by the service switching point (SSP). The SSP is responsible for sending call information to the service control point (SCP), routing the request through at least one signal transfer point (STP) in the Signalling System 7 (SS7) network. SS7 is a digital out-of-band method of transmitting signalling (call control) information in the Public Switched Telephone Network (PSTN). The SS7 network is a packet-switched network carrying signaling data (setup and tear down of the call and services) separate from the circuit-switched bearer network (the payload of the telephone call) in the AIN services network. The SSP asks the SCP where to send the call.
The LEC will determine to which IXC that number is assigned, based on the customer's choice. Toll-free numbers can be shared among IXCs. A customer may do this for disaster recovery or so they can negotiate a better price. For example, a customer may assign 50% of their traffic to Sprint and 50% to AT&T.
Once the LEC determines to which IXC to send the call, it is sent to the IXCs point of presence (POP). The IXCs SCP must now determine where to send the call. Once the final determination of where the call is supposed to go is completed, the call is then routed to the subscriber's trunk lines. In a call center or contact center environment, the call is then typically answered by a telephone system known as an automatic call distributor (ACD) or private branch exchange (PBX).
The subsequent routing of the call may be done in many ways, ranging from simple to complex depending on the needs of the owner of the toll-free number. Some of the available options are:
All of the above routing features are sometimes referred to as static routing features. These routes are put in place and are not usually changed. If changes are required, a customer usually has several options to make changes. A customer can call the IXC or an independent RespOrg directly via a special toll-free number to make changes, or a customer may be able to make changes through direct access to the network via a dedicated terminal provided by the IXC.
From 1996 to 2004, the area codes 880 and 881, as well as 882 starting in 1998, were used as special telephone area codes for the provisioning of international inbound foreign-billed 800-type toll-free services.[8][9]
The service enabled callers in a NANP country to access toll-free telephone numbers in another NANP country. The caller dialed 880 followed by the seven-digit toll-free 800-number. The caller was billed for the international call to the destination country, while the receiver paid the domestic call leg.
Use of this set of area codes was discontinued effective April 1, 2004,[10] when the area codes were returned to the pool of unassigned future toll-free area codes.