Swisscom Callfilter

How the telephone spam filter works

How can you prevent unwanted cold calls? Swisscom’s call filter provides a smart and effective solution. Callfilter blocks 120,000 calls daily and continuously blacklists new phone numbers.

Felix Raymann, 30 November 2017

As if they weren’t annoying enough, the nuisance of advertising calls peaks in the autumn as the annual deadline for changing health insurer approaches. Swisscom’s Callfilter makes short work of spurious brokers and cold callers: launched in November 2016 for the fixed network, the service meanwhile blocks 120,000 unwanted calls daily to 200,000 Swisscom customers. In the first year alone Callfilter blocked 17 million calls across Switzerland. Callfilter is now available for mobile phones.

Adaptive and always up-to-date

The free Callfilter uses a continuously updated black list to block phone numbers. They come from dynamic lists of known spam callers. The list includes the phone numbers of call centres that use spurious sales pitches, call at inconvenient times (before 8 am or after 8 pm and at weekends) or do not comply with the Code of Conduct. The code includes respecting directory listings marked with an asterisk to stop nuisance calls and display of the caller’s own number.

The list also contains numbers blocked personally by fixed network Callfilter users. Customers block around 8,800 numbers daily. These numbers are not added to the black list immediately; they are anonymised and used to continuously improve call filter effectiveness. Callfilter also checks a number of criteria before the relevant number is placed on the general Callfilter list.

Swisscom’s Callfilter currently blocks over 120,000 unwanted fixed network calls daily. With the number of unwanted cold calls to mobile phones steadily increasing, the free Callfilter is now also available on smartphones. Image: Keystone

Smart filter

In principle, Callfilter works like an e-mail spam filter: software in the background checks the incoming call number in real time before a connection is made. If the call is from a call centre the system decides whether it is a legitimate call from a research institute conducting a survey, a support call or an unwanted cold call. If it is blocked, the call recipient doesn’t notice a thing. The caller hears the engaged tone. Callfilter blocks domestic and international calls, although most unwanted calls come from abroad.

Personal black list for the fixed network

If an unwanted cold call reaches a fixed network customer, they can report the phone number by pressing *00# after the call. Customers who feel private callers are a nuisance and whose numbers are not blacklisted can have them blocked on their personal line. Another setting ensures that all anonymous calls are blocked on their line.

Callfilter for mobile phones

Swisscom to launch Callfilter also for mobile phones on 30 November 2017. Using the same system as the fixed network Callfilter, it allows cold calls to be automatically blocked on smartphones as well. The mobile, system-neutral Callfilter can be activated in the Swisscom-Cockpit at any time.

The current volume of calls to fixed network numbers is much higher than those to mobile numbers because brokers think they are more likely to close a deal via the fixed network. In addition, calls to mobile phones are more expensive than to the fixed network. An increasing number of cold calls to mobile phones are being recorded in other countries, however, which will make Callfilter for smartphones more important in the future.

How to activate Callfilter