Direct Inward Dialling (DID) often also referred to as Direct Dial In (DDI) is a feature offered on both in-house PABX and cloud-based telephone systems. It allows incoming calls to be routed directly to an extension without having to go via an operator. This provides convenience for callers and simplifies the running of the system for the business.

By renting a block of numbers from their provider, companies can give each employee their own direct phone number that can be printed on business cards, etc. This allows customers and other contacts to call someone directly, but without the need for a separate external phone line.

Numbers v lines

The quantity of DID numbers doesn’t have to equate to the number of lines in use. If you have, for example, 12 lines on your system, this allows 12 calls to take place simultaneously. However, you can have a greater number of DID options, so if you have 25 employees they can each have their own number, even though there are only 12 lines.

Anyone dialling in while all lines are in use can be diverted to a voicemail system rather than getting an engaged tone. DID lines can also be used to give devices such as fax machines their own number.

Adopting DID streamlines your operation because fewer calls need to be handled via an operator. It also means that if someone is not at their desk, the call can be sent straight to their personal voice mail.

DID number providers

While DID has been a common feature of PABX systems for a long time, many businesses are now turning to VoIP based telephone systems to take advantage of the lower costs and extra flexibility that they provide.

DID can be used in a similar way on IP based systems. When callers ring in from conventional PSTN phones, they’re still able to call extensions of the VoIP system directly. This is because the DID number providers assign the numbers via a gateway, providing a bridge between the PSTN and VoIP networks. The gateway allows calls to be routed between the systems, so calls from a PSTN phone to a DID number get sent to the appropriate phone.

On a PABX, using DID requires an ISDN line and a range of numbers rented from the service providers. VoIP and PABX-as-a-service systems are somewhat simpler in that the technology uses your internet connection, so you don’t need a digital line, but you still rent the numbers from a service provider in a similar way.

Using a VoIP system also makes it easy to divert calls between devices. This means that sales staff, mobile service engineers and so on can have calls to their DID number diverted to their mobile devices when they are away from the office. The number is tied to the individual, with the added benefit that it still gets all of the exchange services including voicemail or automatically re-routing calls when someone is on holiday or the number is busy.