I live in bangalore, india, i got a call from this number 004-420-8792
1030, regularly on a fortnight basis, whenever they used to call me they did it about 5 times in about 15 mins, and couple of calls among them would be from a calling card 004044
or saying private number. And as john mentioned even i heard someone pushing buttons on their phone or something in the background but no one would talk . i knew couple of men living in south london, and the number seemed like from that place and thought they must have turned to stalkers seriously!!!i got calls for a year till i changed the number. never heard a voice!!