It's rather interesting with copper and fiber optic cabling. It makes a difference as to what type of installation one is doing. It's different for long runs for a neighborhood versus all the curves and turns in an install for a company network for instance. It's still not worth doing for home use.
However, with the cost of copper going up, and the cost of fiber coming down; particularly in huge lots like would be used by ISPs per se, it's looking more realistic apparently.Cost of Fiber Optics Vs Cost of Copper - eHow.com
Both copper and fiber optic wire allow data and sound to move along their lengths. Copper wire has a noticeably smaller bandwidth since it was mainly used alongside older land-line telephones needing only voice signal movement. As a result, all the Internet information people crave currently need fiber optics to move the signals faster and more efficiently.
In general, fiber optics cost from 1 to 5 percent more than standard copper wire. This cost factor is negated when compared to the amount of data one line of fiber optics can hold as opposed to copper wire.
Copper wire by nature is heavier than fiber optic. As a result, the lightweight aspect of fiber optic is helping keep underground electrical wiring channels from becoming too heavy or cumbersome.
Don't know when that was written. They really need to note the last time a page that can fluctuate like that is updated. There are lots of pages from years ago where fiber optics is out of sight price wise...
But as HowStuffWorks "How does a long distance call work
Physical wires no longer connect the offices together for each phone call. That system was incredibly expensive. Instead, a fiber-optic line carries a digitized version of your voice (see How Analog and Digital Recording Works for a description). Your voice (along with thousands of others) becomes a stream of bytes flowing on a fiber-optic line between offices. The difference in cost between "a pair of copper wires carrying a single conversation" and "a single fiber carrying thousands and thousands of conversations" is phenomenal.
Lots of considerations...more bandwidth is needed for Internet transmissions than phone calls though...