The problem is literally the
opposite of laissez-faire economics.
Local, state and federal governments all give massive amounts of money to the established communications companies for building out the infrastructure. New competitors can't get these grants, and they wouldn't have a market anyway because local governments award franchises (monopolies) to certain companies.
The above is for physical media (cable and telephone.) It's a little different for cellular, but nobody can afford to up and build a new cellular network. The small operators like Fido and Koodo sublease from the big companies.
To x25064, w.r.t. AT&T being split up again: Unlikely. It's not illegal to be a monopoly. What's illegal is when you abuse your position in the market (e.g. collusion, exclusivity deals, bait-and-switch things where you predicate the sale of a product on the purchase of a complementary good.)
For example, Samsung and co. were convicted in an antitrust suit for fixing SDRAM prices. None of those companies are anywhere close to being monopolies.
AT&T was broken up as a settlement of an antitrust suit, because they were using the profits from their telephone manufacturing monopoly to subsidize their telephone service (making it impossible for any competitors to enter the market.)
Microsoft was convicted of illegally creating their desktop OS monopoly (exclusivity agreements) and abusing that monopoly to damage their competitors (Sun and Netscape.)
Note that the behavior of certain other groups (e.g. RIAA, MPAA) are certainly illegal as well, but they contribute too much to certain politicians.
GoY's Pessimistic Soy Boy Toy