i have a friend who does this for a living. travels all over to service stuff at the top of towers. needless to say, he makes great money doing it.
he tells me some crazy stories.
his take on it, he's been doing it for 15 years:
you need to be in incredible shape, some of the smaller towers (300-1000 ft) are all climbing. he says he can spend 2 hours + climbing a day to do 15 minutes of work.
he says the monopoles are the worst.
and he said that for the first 6 months he worked almost exclusively 1 handed (would not let go with other hand.) - now he says he's so used to it, that it's easy to forget how high you are.
he also told me that he's seen new guys freeze up there, and not move for quite some time. and he says it's all easy until you are above the tree line. anyone can climb the first hundred feet. after that it takes a whole 'nother kind of person.