In the early days of the telephone, the idea that you might be able to dial a number yourself was unthinkable. You called an operator and they connected you to the person you wanted to call, usually by physically plugging a wire into a socket.

As the technology developed and exchanges began to become more automated, it started to become possible to dial another phone directly. The introduction of area codes made this viable on a wider scale.

The first direct dialled long distance call took place in the USA in 1951. The technology came to Britain a few years later with what the Post Office – which was responsible for telephone services at the time – called Subscriber Trunk Dialling (STD). This was introduced in Bristol in 1958, the Queen making the first call. By the mid-1970s the last manual exchange in the UK was decommissioned, making the phone system fully automatic.

Private exchanges

But while the national phone network made it possible to dial any number from any other number without the help of an operator, if you were calling a business, you would still inevitably be met with a switchboard operator who would then connect you to your desired extension.

Private branch exchanges (PBX) or private automatic branch exchanges (PABX) – widely referred to as switchboards – didn’t start to get technology for direct incoming dialling (DID), otherwise known as direct dial-in (DDI) until around the 1990s. This meant that an external phone number could be assigned directly to an extension, so if you knew someone’s DID number you could place a call straight to them without having to go via an operator.

This involved buying a bundle of numbers from your service provider, the software of the PBX then allowing you to assign them to extensions as required.

DID number providers

With the advent of VoIP and PABX-as-a-service offerings, businesses now have even greater flexibility as to how they allow customers to contact them. DID number providers operate as wholesalers and will rent you a block of numbers that will work over a VoIP connection.

Because all of this happens via a cloud service, there’s no hardware costs for the business and no need to accommodate the PABX machinery on site. It also provides a good deal of flexibility as numbers can be redirected as required.

An additional benefit is that you can give your customers a local or fixed rate number, allowing them to call you more cheaply. Many providers will allow you to port your existing numbers over to a VoIP DID system so you can keep your contact details the same.

The big advantage of DID over VoIP is that a number is linked not just to a physical phone extension, it can be diverted to a mobile phone for employees who are on the move. Plus, although a number is linked to an individual, it still benefits from the virtual exchange services such as voicemail, call forwarding and re-routing in the event that a number is engaged.