it's a telemarketing bot - it calls and if you pick up it makes a tone and records on the telemarketers end when you answer and when you done. so they know the best times to call you back to sell you stuff.

annoying bastards

Have rang a few times trying to sell mobile phone and home internet packages have asked not to be called and still they keep calling back.

internet telemarketers

Caller: Active office internet supplier

Sales call