By Ger Ryan, Head of Professional Services, iCONX.

Globally, unallocated number ranges represent many billions of telephone numbers or CLIs that should not be in use, because they have not been put into service with active customers. When traffic is driven to these ranges it often carries risks of arbitrage, negative margins and exposure to fraud traffic, that can impact Telcos bottom line and customer experience. 

Here we explore some of the financial and customer-focused benefits when Telcos pay attention to unallocated ranges. 

Enhanced Fraud Detection 

One thing almost all telecommunications fraud management systems have in common is that they sift through masses of data to identify possible International Revenue Sharing Fraud (ISRF) fraud cases, and alert these to the system users.  

Using 3rd party intelligence to identify unallocated ranges, can significantly improve fraud detection, and provide further confidence for blocking of suspicious fraud cases, where unallocated numbers which should not be in use are active. 

iCONX has partnered with Biaas, a UK based specialist company who have developed the FNRM™ database to improve detection of IRSF fraud related scenarios, such as Wangiri and PBX hacks. With the unallocated data intelligence from Biaas, the iCONX Fraud Management system can detect more fraud cases with confidence. For example – an unallocated range in Belarus +375254 could be used to trigger a higher priority alert rather than a valid Belarus range +375255, meaning fraud teams can better focus their attentions and be more responsive to threats. 

Blocking of traffic involving Unallocated CLIs 

Whether the purpose is to prevent revenue leakage, prevent a bad customer experience or comply with local regulation, there are many reasons why it is crucial that operators can confidently and accurately block unallocated number ranges. It’s also worth noting that some Telcos choose not to block calls, but instead to warn customers of risk – in which case, the examples below still apply in just the same way: 

Blocking Invalid CLIs in Compliance with National Regulations 

Increasingly, National Regulators are making efforts to encourage Telcos to ensure all incoming CLIs are valid – which includes making sure they are allocated. This is driven by a desire to protect consumers from fraud and scam calls. 

In the UK, Ofcom (the Regulator) state that from 15th May 2023, operators are expected to identify numbers that should not be used as a CLI and to block calls involving those numbers. For those Telcos who wish to do their best to protect consumers, a well-researched and accurate unallocated database is exactly the kind of information that is vital for these purposes. More information here.

Blocking Incoming Wangiri Scam calls from Unallocated CLIs 

Wangiri (missed call) attacks have been a persistent problem for years. They work by enticing an unsuspecting consumer to ring expensive destinations, because of an apparent missed call attempt from the expensive number. Traditionally a mobile issue, we are even seeing these becoming more common on the networks of fixed line operators.  

In recent months, there have been many European wide Wangiri attacks using apparent French special numbers beginning with +3382. These numbers will be treated as French premium by international carriers, attracting a cost of at least 25 Euro cents per minute if dialed. However, a review of unallocated numbers reveals that the CLIs being used are not yet live in France, and they do not even have a national rate assigned. These calls could have been prevented altogether by a Telco using unallocated data to inform their blocking. 

Blocking of Outbound Calls to Unallocated Destinations 

Two of the oldest Telco frauds are the ‘PBX Hack’ and the use of Business Lines calling expensive destinations, and both still occur today. The sure-fire way to reduce the extent of losses from these frauds is to block calls to unallocated destinations.  

We have seen many frauds over the years to South Sudan number range +21195. This is listed as Vicacell South Sudan in many price lists, and kept open therefore by many operators. However, the network was switched off in 2018, and the newly unallocated range has been extensively used for many types of frauds with interconnect costs often in excess of 30 Euro cents per minute to this destination. Preventing ranges like this from being dialable will assist with PBX & Business line fraud exposure. 

Further applications – Bill other Carriers Higher Origin Rates for Invalid CLIs 

OBR (Origin Based Charging), emerged in Europe in 2016 when voice margins were starting to decline. The main intention with OBR was to address charging imbalances between carriers.  In Europe, calls originating outside most EU countries are now subject to higher termination rates than those originating within the EU. 

OBR origin charging often includes a higher premium rate for incoming calls with an invalid or ‘non-dialable’ CLI. For example, the unallocated dataset within FNRM™ tells us that a call with a CLI beginning +995 512 might look like a Georgia Mobile, but is actually an unallocated/ invalid CLI.  

Carriers with this unallocated data intelligence will know this CLI is invalid, and most likely is spoofed to avoid higher OBR charges. With this information, Telcos can choose to bill the carrier they receive the traffic from at the higher premium rate. This can work as an additional tool to deter usage of invalid numbers, as well as earning additional revenue for spoofed number ranges that could have been charged against cheaper origin destinations. 

Telecom Fraud Prevention with iCONX 

iCONX Fraud management system is driven by artificial intelligence to combine both inbound and outbound voice traffic analysis. Using the latest technology, industry insight and market leading numbering intelligence, we are expertly placed to help you combat wholesale telecoms fraud for international voice traffic on your network.

Contact iCONX today to discuss how we can help you with your wholesale fraud management needs. 


  • Biaas and the FNRM™ database 
  • Ofcom (the UK Regulator)