Call Forwarding: How it Works – The Feature of Numbers Substitution

Call Forwarding: How it Works – The Feature of Numbers Substitution

Want to see the customer number on the mobile after the call forwarding? Why is it impossible to read in a long and boring, but detailed article about redirection and substitution of numbers with references to laws. We answer the questions: what is it about, how it works, why the outgoing, how much it costs, why we do not do the substitution and how to get around.

What is call forwarding?

Call Forwarding is the transfer of an incoming call when the handset is not picked up. There are conditional and unconditional redirects: in the first case – translation under several conditions, in the second – the translation of absolutely all incoming calls. Conditions such – on employment, on inaccessibility, at no respond, at the input of additional (for automatic telephone exchange).

If the call forwarding takes place inside the PBX – there is no tariffing, but when the call goes to an external number – city or mobile – the call forwarding is paid. And what is important: even if you transfer from the PBX to another number connected to the PBX, then the forwards are paid – the call leaves us and goes through the operator. In most cases, every minute of redirection costs as an outgoing minute. Sometimes the forwarding is subject to separate prices, the price of the package does not apply, and so on. Check with the operator.

Why you need an outbound connection

Redirection is, even if it is not. A common situation: “I will receive calls to the mobile, why do I need outgoing calls and redirects?”. This is a mistaken opinion: if the call goes through the automatic telephone exchange to the mobile phone, redirection works, the call is charged, and the number must be outgoing. Redirecting to mobile or city calls – these are two calls: incoming and outgoing. Therefore, it is important that you have at least two lines and an outgoing connection.

In PBX there is a feature: you can select the number through which the call will be forwarded. By default, the forwarding is perceived as a normal outgoing call and the outbound rules work. However, you will not know which number the customer called. To avoid this, you can specify for each of the numbers – use rules or this number to forward the call.

However, in any of the options on your phone, you will see your external number, not the client. Running ahead is not a fix, but there are workarounds.

Substitution and legislation

The definition of a number when redirecting is the main problem that our users face. They want to see the customer number to call back if necessary. But the legislation of some countries is on the way of business.


To understand, find out how communication operators work. Their activities are licensed, and to become an operator, you need to get a license. The license has requirements, for example, it is necessary to hand over a communication center in country authority body. Difficulties are small – even a business center can become an operator, it is not necessarily a large company like Telenor. Operators do not exist in isolation, they interact with each other through interconnection agreements (interconnect).

Thousands of operators are subject to the same law “On Communications”. It completely regulates activities in the field of communications, and for its failure to select the licenses (need to be checked for each country). Without licenses, other operators will not work with you – it’s forbidden, otherwise, they too will be taken away. And without others, you can not – how to call someone else’s numbers? For an operator, revoking a license is the death of a business, like a bank.

The law  refers to the need to certify software and accounting equipment:

The list of means of communication subject to obligatory certification, approved by the country’s government, includes:

… as well as communication facilities with measurement functions that take into account the volume of communication services rendered by communication operators in public communication networks …

Tracking, dropping, recording and storing calls with a substitute is the responsibility of the operator. In fact, the substitution of the number is not prohibited, but the operator is obliged to react. Violation threatens revocation of the license.

Conclusion: you can substitute, but it’s pointless – the substitution is suppressed. For individuals and ordinary companies, there are no punishments yet.


There are two areas that are interested in restricting the substitution of the number. This is the operators themselves and special services.

Large operators comply with legislation and are forced to conclude international agreements on the exchange of traffic. They send international calls through official channels and pay for every minute under these contracts. Therefore, when a call comes from abroad, they are interested in making calls through the same channels and already paying them. But the call can be sent over the Internet, do not use their channel and do not pay them. Operators lose money on this.

With special services it’s even easier – they need to know who, whom, and how much they called. Therefore, when the number is replaced – some of the information is lost and it is more difficult to find terrorists/criminals.


What is not forbidden is allowed, so in some cases, there may be a substitute. It’s about constantly changing the number that you own. For example, you have a city number for which you receive incoming. And you want the same number to be determined when calling via SIP telephony. If you can confirm the possession of the number, some operators will allow you to substitute it. But incoming from customers will still not be determined.

This is the initiative of the operator and it remains at its discretion. Unfortunately, we will not prompt such operators.


Periodically, among colleagues, the idea is that the substitution will be allowed. We have the opposite opinion – the situation will only get worse. For the second year, the media have been writing about a direct ban on substituting numbers for calls from abroad. The interests are the same: money and security, more about the initiative in the material of RBC.


Theory and practice often diverge. But we have no answer, what happens with the substitution in practice.

All the above applies to telecom, we work in IT. So we run into the lawless often, and we do not make a substitution – the operators do not miss. We do not know how often punished for substitution. And certainly we do not want to know this on ourselves, therefore we comply with the legislation.

How to solve

If you can not show the customer number on the mobile manager, you can search for alternatives. We do not have a ready solution, but integrators offer several options at once.

CRM Call Forward Feature 

The problem with determining the number is really there and some developers of CRM have solved it.

Callback for the manager: the script by the manager number will automatically connect to the last client. And since the call passes through the automatic telephone exchange, the conversation will be recorded and will get into the correct card of the CRM.

Send during or after an SMS call to the number of the manager who answered. In the SMS, the client’s name is from the CRM and the number.

Instead of or together with SMS send the same information to the email manager.

In a pinch, transfer managers to CRM.

These are the main options, just do not stop there and try to find a suitable solution for each customer.