There is no simple, general answer. It is a matter of what materials are available and at what cost. Years ago wooden telegraph and electric poles in many South African towns were reasonably common; creosoted poles were reasonably cheap and lasted for many decades if they survived traffic and fire; metal commonly got corroded at ground level by dog pee. Wood is neither as homogeneous nor as standard a material as metal, but years of experience had supplied the Bureau of Standards with material for specifying effective codes of practice.

Costs of wood seem to have risen faster than costs of metal (not to mention coarse grades of glass reinforced plastics), and electrical practice seems to be favouring pylons far higher, larger, and more vandal-resistant than are practical with wood. Training for erection using mass-produced standard metal components probably is less demanding than training for erection of wooden structures of equivalent scale and complexity.

Simple wooden poles often are more attractive than metal in "the sticks", whereas metal poles had their attractions in urban areas where applications were more complex and the high cost of erection reduced the relative cost of metals in the intensive electric and telephone reticulation projects in towns.

"Telegraph" poles depend on a lot of things.

Think for the question whther some country has 

suitable wood of its own or money to import.

A technical preference might arise from the

possibility to climb on a wooden pole easily

with the aid of some hooks fastened to ones shoes.

And last not least: We did it that way since long, why change?

Georg

PS in Germany there are a lot of concrete poles today.

Wood is replaced more and more. Telephone is below soil,

exept mabe some lonely farmhouses.

There is a railway from Münster/Westfalia to Rheda-Wiedenbrück, not

owned by State railway, there new wooden poles were erected

with "telegraph" wires about 1995, I think that is the last  railway with

this in Germany. I guess this is a kind of  technical monument.

Here in the US, most all the utility poles along the streets and road sides are wooden.

Many street lamps and traffic signals and highway signs, are on metal poles.

In Manhattan, and I'll guess London, all the utilities are underground.

It's all about cost.

Wooden cheapest.

Metal more expensive.

Underground very expensive.