Telecoms glossary • D
DID (Direct Inward Dialling)
A direct number for everyone who needs one, arriving over the trunks you already pay for.
What is DID (direct inward dialling)?in VoIP and business telephony
1. Direct inward dialling gives an individual person, desk or department its own public telephone number that rings straight through, with no physical line behind each number. Every one of those numbers arrives over the same trunks or cloud subscription you already have, and the phone system maps each to the extension it should ring.
2. DID is the inbound half of a number. The outbound half is the caller ID your system presents when that person dials out, which is configured separately and is the reason a direct number can ring in while the wrong number shows on the way out.
How a DID reaches the right desk
The mechanism is a lookup, not a wire. Nothing physical changes when you add the hundredth number.
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Your provider allocates numbers
Licensed operators hold ranges from the national numbering plan and assign you numbers out of them. You are given numbers, not lines.
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Each number is mapped to a destination
In the phone system’s portal, a number points at an extension, a hunt group, an IVR menu or a queue.
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The call arrives with the dialled number attached
An inbound call carries the number the caller dialled in the SIP request. The platform reads it and applies the mapping.
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Capacity is separate from quantity
What limits you is concurrent calls, not how many numbers you hold. A hundred DIDs on six channels is fine until a seventh caller dials in, which is why the two are quoted separately.
That last point is the one that catches buyers out. Numbers are usually cheap and recurring; channels are what you actually size.
Which South African number range to ask for
The prefix you choose signals something to the caller and decides who pays. ICASA’s numbering plan sets out what each range is for.
- Geographic, 010 to 049
- Tied to a region: 011 Johannesburg, 012 Tshwane, 021 Cape Town, 031 Durban. Still the strongest local-presence signal for a business selling into one metro, and the range most customers dial without thinking. Caller pays their normal rate.
- 087, non-geographic VoIP
- Released by ICASA for voice over the internet services. Location-neutral, which is either the point or the problem depending on whether you want to look local. Widely used for national businesses and cloud phone systems.
- 080, toll free
- The caller is charged nothing, whichever network they call from. You carry the whole cost. Reserve it for the numbers where you genuinely want the barrier removed.
- 086, inbound services
- A range for services used only to receive calls, which is where shared-cost numbers sit. Check what the caller is actually billed before you print it on anything, because customer perception of this range is not always favourable.
Our guide to toll-free numbers in South Africa goes into who pays what on 0800 against 0860 in detail.
What else a block of DIDs buys you
Direct numbers are the obvious use. The useful ones are the configurations you would otherwise pay for as a feature.
- Campaign attribution
- Put a different number on the website, the vehicle branding and the print advert, point all three at the same queue, and the call records tell you which spend produced calls. It is the cheapest attribution any business will ever buy.
- Department routing without a menu
- A published accounts number that lands in the accounts queue removes an IVR step for the callers who already know where they are going.
- Location independence
- A DID follows the extension, not the building. Someone working from home answers their direct number on a softphone and the caller cannot tell. See remote extensions for how that is set up.
- Time-based handling
- The same number can ring differently after hours, at month end or during a promotion, because the routing sits on the platform rather than in the number.
Ask this before you order numbers
Ask who the numbers are registered to, and get the answer in writing. Numbers issued out of a provider’s range are portable under South Africa’s number portability rules, but the practical experience of porting varies enormously between operators, and the time to establish that is before you print them on a fleet of vehicles, not after. Our note on number portability covers what porting actually involves.
Then ask what each number costs per month, whether unassigned numbers in an allocated block are billed, and what happens to the block if you take only part of it with you. A cheap per-user price with expensive per-number charges is a common way for a quote to grow after signature.
About this entry
Definitions are written for South African business buyers and checked against primary sources – provider documentation, standards bodies and ICASA – not vendor marketing. Reviews are independent and sponsors are always disclosed. Read our editorial policy and scoring methodology.
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