Communications providers

This page is aimed at Communications Providers, some of the language used may not be understood by people who are not in the telecommunication industry.

Helping your customers move from Text Relay to NGT

As well as providing the facilties found in Text Relay NGT gives your customers more. NGT uses specific TextNumbers so callers don't need to use the old 18002 prefix. Your customers can also use the NGT Lite to contact friends, family and businesses on the move, with a laptop, tablet or smartphone. When used on an internet connected device NGT Lite enables your customer to see their text conversation in parallel with the phone call.

However if your customer doesn't want to change, their textphone will still work with NGT.

Getting ready for NGTS

You don't need to do much.

There's no change to the way BT sends you billing information or the way that you manage any rebate calculations for your customers' bill. You'll also still be allowed to charge only the equivalent cost of a standard voice phone call and not pass on any conveyancing, facility or Interconnect fees to your customer.

What you need to do

We'll manage the new 03 and 07 TextNumbers but you'll need to make sure that calls to them are routed to NGT. Information has been provided through the standard BAU routes via BT Wholesale.

What you might want to do

  • Think about telling your customers how they can get NGT Lite and perhaps offer it as a download from your website.
  • Include users' NGT TextNumber in their phone book listing.
  • Put a link to NGT website on your website.
  • Make sure that your front-line staff are aware of NGT so that billing enquiries or questions about particular packages and tariffs are directed to the right team within your organisation.

Regulatory obligations

Under the General Conditions or Entitlement (GCE) section 15, all UK Communications Providers are required to provide:

  • access to a relay service
  • call progress announcements in text
  • equality of call charges.

BT Suppliers' Information Note

Click here to view/download the NGT SIN 359

NGT prefixes

NGT prefixes start with the digits 1800 and require other digits for a call to be set up successfully.

Presented numbers

When making a call through NGT your customer could use the 18001 or 18002 prefix to dial any phone number from three digits to a full international phone number. The prefix plus all the dialled digits must be presented to NGT. As the digit string is not a fixed length you must make sure that customers are given sufficient time to dial all the digits. This is normally done by the local exchange waiting for around 4 seconds after the last digit and before processing the call. This of course only applies to fixed phone lines where the caller dials individual digits.

The diagram below shows that the NGT 1800X prefixes are only used on the incoming leg of the phone call. The destination network will be presented with a standard voice phone call.
graphic showing that the 18001 prefix is stripped from the callers dialled digits


18000 is the equivalent to 999/112 for customers who use real-time text and should be treated as such e.g. priority routing, repeat attempts, etc.

When a customer dials 18000 CPs must append their Interconnect Identification (II) digits and, where appropriate and agreed with the 999 Service, any zone or cell ids that are appended to 999/112 calls.

When the call is presented to the NGT Service 18000 is replaced with 999 and the call is connected to the 999 Service with a relay assistant facilitating the call.


  • For CPs who don’t use BT as their 999 Service provider separate individual arrangements are in place.
  • 18000 calls are filtered to detect misdials e.g. 1800010207… will be rejected.
  • If a customer dials 18001 999 or 18001 112 NGT will route the call to the BT 999 Service. However the call into NGT will not be seen as a priority call and if there's congestion within the phone network the call could be rejected before it reaches NGT. Once the call reaches NGT it will be handled as an emergency call but as there will not be any II digits the 999 Service will not be able to identify the originating network. This could delay or even prevent location information from being passed to the emergency services. For these reasons CPs should consider translating 18001 999 and 18001 112 to 18000 and append their Interconnect Identification (II) digits in order to improve the availability of the location information.
  • CPs must only advertise 18000 as the number for their customers who use real-time text to call the emergency services.
  • 0800 112 999 is the old Text Users' Emergency Scheme number. While this number still works it suffers from the same problems a 18001 999 and 18001 122. The number should not be advertised.


18001 is the NGT Prefix for customers who use real-time text.

The 18001 prefix must be followed by the destination’s full phone number.

Customers should be able to dial any telephone number accessible from phone line e.g. geographic, mobile, premium, international, etc. CPs must signal call barring in ISUP BSMs or block any barred numbers e.g. 1800109…, etc. before presenting the call to the NGT service.


18002 is the NGT Prefix for customers who want to call someone who uses real-time text.

The 18002 prefix must be followed by the destination’s full phone number.

Customers should be able to dial any real-time text user’s telephone number. CPs must signal call barring in ISUP BSMs or block any barred numbers e.g. 1800109…, etc. before presenting the call to the NGT service.

Access to voice services such as the speaking clock or call return is blocked by the NGT Service.

Access numbers

NGT can also be accessed through the following numbers:

  • 18001 + phone number
  • 18002 + phone number
  • 18000 + Interconnect Identification digits
  • 0870 240 9598 (calls to this number cost 1p per minute plus your phone company's Access Charge)
  • 0870 240 5152 (calls to this number cost 1p per minute plus your phone company's Access Charge)
  • 0330 670...
  • 0777 789...
  • +44151 494 1260
  • +44151 494 2022
  • 0800 500 888
  • 0800 7311 888

When using SMS on a mobile

  • To send an SMS text to the emergency services send it to 999 or 112


Where a shortcode such as 150 is used to call the CP’s customer service this must be translate into a number that’s accessible from the BT network e.g. 18001 150 translated to 18001 0800 800 150.


NGT uses both the Calling Line Identification (CLI) number and the Calling Line Identification Presentation (CLIP) number. This section describes which number is used by which part of NGT.

For most calls the CLI and CLIP are the same number. However with business systems it's not unusual for the CLI to be a billing phone number while the CLIP is the business's switchboard number.

The CLIP is the number that appears on the called telephone display and is used by services like 1471 Call Return.


NGT bills the Communication Provider and produces a Call Data Record (CDR) based on the call's CLI.

Call rejection

NGT will reject a call if the call's CLI is not provided, if the CLI is an 08 number, or the CLI is an 09 number.

Linking a phone number to the NGT Lite app

NGT links phone calls to the NGT Lite app using the CLI number.

As mentioned above some business calls have different CLI and CLIP numbers. This means that the NGT Lite app is linked to the CLI i.e. the billing number, however a call to the business will dial the 18002 + CLIP which is the switchboard number. In this circumstance the NGT Lite app will not see the call.


NGT associates a TextNumber with the call's CLIP.


For 18000 calls NGT forwards the call's CLI to the emergency service.

Withholding the CLI

More correctly it's the CLIP that's withheld, the withheld flag is passed through NGT and on to the destination.


As a Mobile Network Operator (MNO) or Mobile Virtual Network Operator (MVNO) you're required to provide your customers who are deaf or speech-impaired with SMS access to the UK emergency services.

The emergencySMS enables your customers to send an SMS text messages to 999 or 112. The message is then routed through BT's standard voice 999 service and on to the UK emergency services.

For your customer to be able to use the eSMS service you need to ensure that SMS messages sent to 999 or 112 are routed to Dialogue Communications Ltd who act as the aggregator for the emergencySMS service.

Updated: 06 July 2016