I'm afraid I didn't read TFA, so apologies if I'm getting the wrong end of the stick. Also it's been 20 years since I worked in PSTN stuff. But at least at th

I'm afraid I didn't read TFA, so apologies if I'm getting the wrong end of the stick. Also it's been 20 years since I worked in PSTN stuff. But at least at that time, the security in the protocol was ridiculously lax. IIRC, with PRI there was literally a bit that you set to say that the originating number was checked and was legitimate. Every other switch on the way through would accept it blindly. In most areas it was illegal to set that bit unless you were a telco. It was also illegal to sell equipment that set that bit unless you were selling it to a telco. But... it's not that hard to hack. Someone who's more current can probably give you better information. As to why nobody does anything about it... well.. why should they? They literally don't care. The equipment manufacturers aren't going to change the specs (because it's pretty darn hard to change specs and they are all trying to screw each other over in the specs anyway). The telcos aren't going to demand that the specs are changed because people are making telephone calls -- exactly what they want. It's only if the governments demand the change -- and it will take laws to do that (even then, I imagine that it's cheaper to lobby against the law than to change the equipment -- you have absolutely no idea how crappy those systems are).