Along with the 3/5ths clause, the USPS is another example that just because something's in the Constitution, it doesn't make it a good idea. The government has no business being in this outdated industry.
Actually it's a case of a constitutional provision being viewed in a strict constructionist form rather than its actual intent. It would be as if the provisions allowing for an army and an navy were viewed to preclude having an air force.
There is no reason why those provisions could not have been used to provide for greater government involvement in telecommunications as was the case in a number of other countries. The purpose of the clause was to ensure that communication could be reliably be made between any two people in the US, no matter where they may be.
While snail mail has declined in importance, the availability of a universal carrier of the same, available to all, has not.