Fed Ex delivers
everywhere in the U.S. I assume UPS does too. If you have information to the contrary please provide it.
A constitutional amendment would NOT be needed since the the Constitution merely authoritizes, but does not require, the Post Office. The Constitution DOES NOT authorize the current postal monopoly. IMHO, this monopoly is unconstituional.
BTW, if you want more on the sordid origins of that monopoly read up on Lysander Spooner who was so successfully at competing with the postal service (including lower prices and his own Sunday delivery!) that the government shut him down. For more on Spooner, see here.
I never said they didn't. What I did say, please read carefully, if UPS or FedEx were given the contract to deliver letters and other first class mail, they'd run into the same problems as the USPS. Now as they are private companies, without a stipulation from the gov. that they have to deliver letters everywhere, they'd run into cost problems like the USPS. As private companies without the obligation, they can stop delivery of unprofitable mail i.e. letters. As they, like the USPS have union workers, they can go strike as UPS did in 1997. Without the USPS as a backup, billions of pieces of mail would have gone undelivered. The military, another government agency, would have had to deploy people to deliver the mail.
Now if you can come up to a solution to make sure the mail always gets delivered using private business with the possibility of strikes, decisions to cancel delivery of unprofitable mail, or the company simply ceasing operations period, (and after you've passed that amendment getting rid of the USPS), I'm all ears.