Combatting telemarketing and unwanted calls with voip

2020, Jan 08    

Telemarketing and unwanted calls have become a HUGE issue over the years. Traditional home phone users were never given any real power over call control in most instances and if they did they were still limited and cost prohibitive in the long term. Paying $13.95 a month from Bell for “Call Answer Message Manager” ie voicemail seems absolutely absurd considering that is a standard feature on voip. You can easily get 3 or more months of voip service for that price.

Most voip companies that are do it yourself such as offer many options for users to control their voip service as they see fit. I’ve used the tools provided to create a system that drastically reduces the call volume of what I consider junk calls.

The high level overview is as follows:

  • A call is received
  • Is the number a known wanted call?
  • If so pass the call and ring the phone
  • If not, offer a challenge to prove you are a human and if passed ring the phone

This type of call flow blocks 99% of unwanted calls in a heartbeat and I’ve been running this for some time now with great success.

I’ve set this system up using but you may also implement it on any other voip providers or setups that offer the same tools.

The first step is to create a ring group which are all the devices you want to ring upon receiving a call from your number (did).

The second step is a whitelisted phone book of all numbers that you want to bypass this system.

Setup as the following on the portal under did numbers/CallerID Filtering:

type of filter : all phone book
did to apply filter: your_phone_number
routing : my_created_ring_group
note : whitelist phonebook

The third step is to create an ivr (interactive voice response) ie. press 1 to contact sales.

Firstly you create a recording of the ivr greeting and prompts that you want. I use the following:

Press 1 if you are not a telemarketer otherwise press 2.

You’ll need to record yourself saying this or use some text to speech software and save this as a wave file. Upload this file to the portal under did numbers/recordings.

You want the challenge question to be said early in the message so that when a telemarketer calls they usually will not hear the initial “Press 1” as there is usually a second or two before they are connected to the automatically dialed call and they won’t hear it. They will only hear the last part of the prompt and usually disconnect. In some instances they also cannot press any buttons to respond due to the way their automated calling software is configured. Either way, they wont pass this phase.

Under the did numbers/digital deceptionist (IVR) setting on the portal create an entry such as this:

name: telemarketer prompt ivr
recording : telemarketer prompt (the wave file you previously uploaded)
time out : 5 seconds
voicemail : use account voicemail

digit : 1
ring group: my_created_ring_group

digit : 2
system : hangup

You now implement call forwarding of all calls directly to your ivr such as the following under the portal:

did numbers/manage dids
edit did
routing/ivr (telemarketer prompt ivr that you just created)

You may also wish to set a list of blacklisted phone numbers. This is useful if you have people always calling from the same number.

Under the did numbers/callerid filtering section of the portal you fill in the appropriate information and change the routing to system/hangup. The great thing about the system/hangup in this case is that it does not cost anything yet provides a cdr (call data record) in your call logs. I previously had the system/number has been disconnected which costs a fraction of a cent on each call but made no difference as the same numbers would continually call even with this tone and message being played every time the line was connected.

All is completed and you will now receive fewer annoying phone calls.

The detailed call flow is as follows:

  • A call is received by
  • The number is checked against your whitelist/blacklist phone book
  • If the number is on the whitelist the call will pass with no challenge
  • If you have setup a blacklist with appropriate options the call will be hung up immediately, logged and cost nothing on
  • If the call is not on your whitelist it will be passed to the ivr
  • The ivr plays the message “Press 1 if you are not a telemarketer otherwise press 2”
  • If there is no answer for 5 seconds the message is played again; this is done a total of 3 times and then hung up
  • If a 1 is entered the call is passed along to the ring group and all devices ring
  • If a 2 is entered or nothing is entered after ~60 seconds the call is hung up


You may notice a slight increase in cost (pennies) as this depends on the length of the ivr prompts and if some robocallers get stuck within these prompts.

Real life telemarketers cold calling (rare) can still bypass this setup as they are physically pressing the appropriate button and passing the challenge/response system. I’ve yet to see this happen.

Hospitals, fire or police may use a caller name of “Unavailable” and caller id of “Unavailable” so they will always force the challenge/response system.

A similar issue will occur on wanted automated callers such as school closures that would normally call and leave a message. You will have issues with call back services such as a banking callback verification that would normally call you back and provide a code over the phone. In this circumstance you will need to review your calls logs and manually add that number to your wihtelisted phone book.

These issues are a small price to pay for protection that is offered but you must be aware of this.