It may also never have had a legal challenge. we may very well live to see a day where taxing communication is rendered... illegal.

Things change. Remember 30 years ago where people could smoke inside a grocery store? How mind-warpingly fast things can change right?

Do you really mean you pay both the telecom subscription + some kind of state/federal tax that depends on how much did you speak/download?

I certainly don't and never did, this probably differs between countries.

AFAIU I pay fixed surcharges per account but I fail to see how, say, a per-SMS tax would violate the First Amendment while taxing each individual sale of a newspaper does not.

In the U.S. we also have a constitutional right to freedom of travel but that doesn't make a gasoline tax unconstitutional.

Generally speaking, the First Amendment prohibits the government from regulating the content of speech, not the speech itself.