Why do receive voicemail with tones, recording of the sea or trains or other strange noises?
You might occasionally receive calls and especially voicemails to your toll-free number that contain recordings of tones, or even crashing waves and steam trains.
Generally, these are from numbers you do not recognize and are actually from malicious 3rd parties.
When someone calls a toll-free number, there is a charge paid by the toll-free number owner to the provider initiating the call. Malicious parties are able to set up systems where they receive a portion of the toll from the initiating provider when they make calls to toll-free phone numbers.
Malicious parties are therefore incentivized to make large amounts of automated calls to toll-free numbers.
This issue not particular to Vumber, and is a form of fraud and is an industry-wide issue for all toll-free phone number providers.
You can safely ignore these call - they are not legitimate calls and we would not suggest calling these numbers back, as it might promote further calls of the same type.