One big difference between unsolicited mails and hoardings are that they are non-intrusive, most times. But telemarketing is very intrusive and disturbs your normal activity.
Out of every 100 calls they make, 99 would have been a disturbance and that would have got conveyed to them. But still they keep doing it. If someone cannot correct themselves after knowing they are doing nuisance, sometimes we will have to teach them the hard way without offending them.
