Re: @Voland
I have my SIP with A&A ISP, not a single nuisance call in past 3 years (i.e. when I moved to SIP). And the reason to switch was, you gussed it, an awful volume of nuisance calls on my landline. What annoys me now is that, landline or not, BT is still making profit from me, because they are the network operator.