An electrician buddy of mine has an electrical wire stripper and he feeds the wires in and they automatically strip the coatings off for him, not sure of the brand but he does odds and ends left over. For phone wire its not worth attempting that, they really don't dock much at the scrap yards for it not being stripped first. As for even worrying about stripping the wire, the scrap price is so high unless you've got truck loads of it, cash it in the way it is and walk away with a check in hand, way more than you'd have gotten for even stripped wire a few years ago, or at least thats what we do, take it in by the dump truck load as is.