There is no void (air) inside the cable, and the pressure is even all the way around - the only crushing you can do is move the atoms closer to each other. (Compress actually, not crush, and iron is basically incompressible.)
"moving the atoms closer to each other" is what I was talking about; under some circumstances, that could manifest as a shift to a different crystalline structure. (If you search for information on high-pressure crystalline phases of materials, you'll find a lot of interesting things.) "Iron is incompressible" is often a useful approximation, but no material is actually incompressible (that would entail, among other things, faster-than-light propagation of shock waves and infinite hardness) and many day-to-day materials are less compressible than iron. Glass, for instance.
Most metal objects do actually have voids in them, but you can manufacture metal objects that don't, and it's not clear that having voids in your cable would cause it to be damaged by pressure.
