They abandoned it to the building owners. Once when there was a building bankruptcy, the building was sold, and then the phone company came in wanting thier PBX equipment after the sale. The telco didn't get the PBX system, cause they didn't claim it before the sale. Supposedly, the FCC is going to come out with a ruling regarding this issue, but I don't know an anticipated date. I suppose, under colocation agreements for riser access.
Inside wire is owned by the tenants during their tenure of the location.