In addition to conductor thickness not being a sole direct factor in bandwidth (the interconnects carrying 32 Gb/s PCI-e or Thunderbolt are much thinner), stand

In addition to conductor thickness not being a sole direct factor in bandwidth (the interconnects carrying 32 Gb/s PCI-e or Thunderbolt are much thinner), standard telephone wire is the same or greater than Cat 5e. Most telephone interconnects will be at least 24 AWG, some short run cables may be 26 AWG (same as Cat 5). Really old interconnects will often be 22 and even as high as 18. And the thing is, these are usually worse from a high frequency transmission line standpoint as they weren’t designed for anything above 4khz voice. Poor noise rejection, cross talk, poor loss characteristics, and inconsistent termination are the more challenging issues in pressing high speed out of the phone network.