From the phone pole wiki:
In 1844, the United States Congress granted Samuel Morse $30,000 to build a 40-mile telegraph line between Baltimore, Maryland and Washington, D.C.. Morse began by having a lead-sheathed cable made. After laying seven miles underground, he tested it. He found so many faults with this system that he dug up his cable, stripped off its sheath, bought poles and strung his wires overhead. On February 7, 1844, Morse inserted the following advertisement in the Washington newspaper: “Sealed proposals will be received by the undersigned for furnishing 700 straight and sound chestnut posts with the bark on and of the following dimensions to wit: ‘Each post must not be less than eight inches in diameter at the butt and tapering to five or six inches at the top. Six hundred and eighty of said posts to be 24 feet in length, and 20 of them 30 feet in length.
The 35 ft pole was the basic standard and goal of the forestry efforts to wire up the world.
As with railroad ties, use of concrete replacements supplemented the lack of available resources to do the job with trees alone. Then there was the other tree limitation – trees don’t grow to the sky.