Intelligent Solutions

Intelligent Caller Rejection – Protect your customers from nuisance calls

Simon Woodhead

Simon Woodhead

10th June 2014

Unlike some competitors, Simwood has no tolerance for nuisance calls being made from our network, but unfortunately our customers continue to receive them coming in. Today we’re pleased to announce the first steps in preventing this.

Anonymous Caller Rejection (ACR)

As Communications Providers our customers have a legal obligation to provide end-users with what BT and others call “Anonymous Caller Rejection”. To help our customers comply with this more easily, it is now available network-side and configurable per number. It is available on any Simwood number or numbers using our Virtual Interconnect Inbound service.

We will charge £0.10 per number* per month that this is configured on. BT charge single-line retail users £4.75 per month (see OFCOM’s comparison for others).

There is an assumption underlying ACR that Nuisance Calls come in the large-part from Withheld numbers, and to that extent ACR helps.

However, according to BT’s own website:

Anonymous Call Rejection will not block calls where the system cannot obtain the identity of the caller and the message “Unavailable” is delivered. This would mean that the call is coming from a network that does not support Caller Display and Call Return type services.

So ACR will screen many public utilities and large businesses due to the configuration of their phone systems and in doing so will also pick up onshore call centres who withhold their number. It will specifically not pick up calls where rather than “withheld”, the Caller ID is not there or is invalid, or calls coming in from overseas.

We find that the majority of the nuisance calls ignore the TPS and are not made from legitimate onshore call centres, but rather less scrupulous organisations both onshore and overseas. Calls from these, which are arguably the most intrusive and threatening kinds of Nuisance Calls, will not be picked up by ACR.

Intelligent Caller Rejection (ICR)

Intelligent Caller Rejection is another Simwood first, and is a step towards solving the actual problem that, in our opinion, ACR fails to adequately address.

Simwood’s Intelligent Caller Rejection (ICR) will filter out calls where the Caller ID is invalid or missing, whether or not it is merely “Withheld” from the end-user. International and domestic calls are allowed, if their Caller ID is valid. If used without ACR, calls with valid Caller ID that is simply Withheld will be allowed through.

This works by virtue of us being a fully SS7 interconnected network operator. At this level there are two caller IDs, one which is presented to the end user and one which is shown to or withheld from the end-user, and another for network use. Where the call originates with a bona-fide network these should both be set properly but are often missing or invalid on Nuisance Calls.

ICR will by default play a basic message (just like ACR) to rejected callers, informing them why their call has failed. In our opinion for genuine Nuisance Calls this simply encourages the criminal (they are a criminal if ignoring the TPS registrations) to spoof a valid caller ID and try again. We know first hand how distressing and troublesome it can be when they do so!

Accordingly, ICR can also be configured to return a Busy signal rather than a message, which will encourage the caller to move on. As a harder rejection it can instead return an Unallocated Number error. The latter will hopefully result in no further attempt to call back and potentially the number being cleansed from the caller’s database as they assume it to be incorrect.

Customers configuring these more aggressive options do need to be aware of the potential for false positives (e.g. legitimate callers with mis-configured equipment) being unable to get through with no explanation why. For this reason we will include any ICR and ACR calls in the routine “blocked calls” notifications we send and encourage customers to build process around them, perhaps reporting to end-users by email when calls have been rejected. It is important though that end-users are aware of the potential for legitimate calls to fail in certain circumstances, even though those circumstances should be fewer than for ACR.

ICR can be configured today through our API and will be charged at £2 per month per number it is set on* regardless of number type. To our knowledge it is unique in the market-place and will be highly desirable to end-users once they understand or experience how basic ACR doesn’t actually solve their problem! They need no special equipment and we think it’ll be a valuable service for you to offer them.

Subject to customer demand, as indicated by service take-up, we have a number of ideas to further enhance ICR and provide more targeted blocking.

Example configuration

ACR and ICR are part of our Advanced Inbound Configuration and as such will work with both fixed line and mobile services, and can be configured at the per number level or as a default configuration*. It is configured as an option as below:

   "options": {
       "acr": true,
       "icr": 486
   "rules": {
   "routing": {

For more configuration information, please see the API documentation.

* customers applying these settings to an account’s default configuration will be charged £500 per month for ICR and/or £100 per month for ACR.

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