I work at a fortune 500 company. This number calls the company and after I say my greeting, it sounds like a button is pressed and they hang up. I have had the same thing happen from different numbers right in a row.
Today 28.10.2015 at 10:56 GMT I've got a call on my mobile phone which was identified as originating from +4247385021. I said "Hallo?". After a pause there come a voice which sounded as female with heavy accent which asked "Is it [they used just a name - no Mr or anything else! And pronouncation was distorted]?". I said "Yes, who is it?" "I'm calling from [something unclear but ending similar to 'hotel']". I said "What? Can you say it again." "Sorry, wrong number". The line went silent but was not disconnected for a few seconds. I've continued asking "Who is it?" until line disconnected.
According to the various sources which I've checked the international code number "+424-" is "Unassigned". Prefix "+42" is currently listed as "Discontinued" being former Czechoslovakia (now country is split and "+420-" is Czech Republic and "+421-" Slovakia). The only other assigned code in this group is "+423" for Lichtenshtein and all other i.e. +422, +424, +425, +426, +427, +428, +429 are "Unassigned".
Thus, question is how phone call identified as originating from +424... can be technically made? Skype is blankly refusing to start dialing this number as it's prefix does not exists.