Client in a large residential building signs up for FiOS. It's a building where the ONT is the MDU type. Requires 1 x coax (video) and 2 x cat5 (data and voice) from the ONT located somewhere in the building to the apartment's demarc point.

FiOS techs come to install and can only locate 1 coax and 1 cat5. So, we agree to provision video and data for the time being while we sort out the missing cable.

Turns out that the cable is totally MIA, and both FiOS and the building say it is on us to run a wire from three floors away where the ONT is located.

Say, what!? Does this make any sense? How is this supposed to work? Does it depend on the specific agreement that the building and FiOS entered into when FiOS was first brought into the premises? Does a telecom provider have any Federal or State legal obligations in this regard? (This client is in NY.)

(BTW, new ActionTech routers require all 4 pairs for data. Luckily, we did manage to come up with a workaround to get voice deployed. Still would like to know how this is supposed to work.)

Not understanding the question.
Are you saying that: They are telling you to run that cat5 wire 'for free'. Is it because you originally wired the building and forgot to do that run?
Just not understanding what is exactly going on.

Ok, when I say it's on "us" to run the wire, I mean my client. I am acting as the client's rep in the matter, which is why I chose that word.

Basically, Verizon is telling the apartment owner to take up the missing cable with the building, and the building is saying that the apartment owner has to arrange and pay for the cable to be run, even though other apartments in the building seem to have the required cables already in place.

I guess in thinking about it, Verizon most likely has an agreement with the building only to be responsible for infrastructure up to the ONT. That makes this a building issue, and therefore less interesting than I originally thought.

OK got it.

Yeah, it sounds like a typical builder. It paid cheap money to have the electrician run the low voltage wire, and of course they missed some things. The builder knows it's going to be expensive to retrofit now and wants to skate on the cost.

Nothing new here.
Comes down to how bad the apartment owner needs that cable in place and how bad he wants to fight the builder on it.

How is this your problem, or more importantly, why are you getting involved?
Your conversation with your client should go something like this:
"Mr. Client, while I can't advise you on your rights or responsibilities as I'm not an attorney, I will be happy to evaluate options and costs for running the missing cable regardless who ends up paying the bill."

A key part of the value proposition I offer my clients involves acting as their "CTO for the home." To support that, I need to be smart on topics like this - not to give legal advise, but to paint a clear picture of the lay of the land. The required time and attention is reflected in my pricing.

What I'm reading he has one coax and 1 cat5 coming in.  Because he chose to go with Fios, he needs 1 coax and 2 Cat5.  Yes, it's on him.

More importantly, he'll have to get apartment manager approval before he runs the additional Cat5.  If they say no.  He's out of luck.

We don't have Fios where I'm at....Isn't it VOIP?  If it is, why does he need more than 1 coax and 1 Cat5?    

it is voip, but the voice is converted to pots dial tone at Verizon ONT (optical network terminal) which is typically located in equipment room/area.

all 4 pairs connected to what? ONT? Is the router POe powered from ONT? Also, how did you deploy voice with existing infrastructure?

All 4 pairs on Cat5 from ONT to WAN port on router. It is not POE - just Gigabit.

It turned out there was a spare coax in place, so we ran the voice (just 1 line) over that wire. All we did was solder twisted pair to the coax on either end. Made me nervous, but the phone rang/answered/dialed/etc. and call quality was clear. Think we're headed for trouble on this?

Maybe.

If all the other apartments have one coax and 2 cat5 coming in, and the other apartment owners did not individually pay for those runs, then it's on the building to pay for it. What did this tenant do, individually, that puts his having the same facilities as everyone else on his dime?

If it's not apartment owners but lessors or renters, then it's even more on the building unless the building is going to pay the renter, when they move out, for the percentage of the CAT's remaining life that the renter won't be able to use, but paid for. Ridiculous? Meant to be to make the point that it's on the building. For that matter, even if it's apartment owners, this point could be made to highlinght who is responsible.