This is random but I don't know anyone under 26 that has a landline. Just a cell phone. So when those are gone, are they just gonna sit in the ground?

They will be re-purposed. Actually, they (telephone lines) are already being re-purposed. Many people connect to the internet at home via DSL, which uses phone lines. AT&T provides television programming via fiber-optic telephone lines (U-Verse).

I think there will always be a purpose for landlines for business use as they have many advantages over mobiles. Definately less and less need for domestic users though.

I think at some point they will just be lying there in the ground. Obsolete like a lot of things from the past.

or perhaps benevolent governments around the world will use them for surveillance, the same way they have put GPS's in every cell phone for your protection!

I have a land-line. (It comes with the rent)

The rebels will use them to tie up the government officials, and to whip radiation mutated domesticated cats pulling trailers of scrap metal and rubber across the dry desert high lands of Norway.

lol quite the picture you paint...

One of the big issues in the development of the internet was that the telephone line was incapable of transmitting enough information to make the internet accessible to all. This was overcome by cable and new DSL technology. It is infinitely valuable to have some cable going into your home as this is going to be the foundation of any new technology. I have no doubt that phone lines will be used for various reasons for many decades to come. It's use as a landline telephone is atrophying especially with the increase use of cell phones and internet phone tools.

That wire is still very valuable. It goes into every home in the united states which makes a lot of technology more feesable. It wont be wasted I can assure you of that. At least until wireless hotspots cover the nation.