Do you know what kind of phone lines these are? If they're regular analog phone lines, then extending them is trivial. In fact you may only need a single extension. Regular phone lines are one twisted pair. The 4-conductor phone jacks in most homes or offices carry two phone lines (center two conductors are main line, outer two conductors are the second line). So you just extend one line, and wire the two pairs to a two-outlet phone outlet.
If these are digital phone lines however (typically office phones with features like extension numbers, forwarding, hold, multi-line, etc), they may be running on two or even three twisted pairs (4-conductor or 6-conductor lines). Not all office phones with these features are digital however. You can usually (but not always) tell by looking at the connector on the phone itself, and count how many contact pins it has.
Generally distance is not a problem. Cat 3 phone line is good up to several km. The twisted pair rejects noise.
https://en.wikipedia.org/wiki/Differential_signaling
bill001g :
Next most time the building codes require you to run what is called plenium cable in a drop ceiling.
Plenum cable is required when the air space above the drop ceiling is part of the ventilation system (called a plenum space). e.g. air from the air conditioning comes out vents in the ceiling. But the return air vent is located in the plenum space.
If the air space above the drop ceiling is dead space (non-ventilated), then you can toss whatever low-voltage cables up there that you want. Although you shouldn't do anything stupid like laying cables across light fixtures which might heat up.
https://en.wikipedia.org/wiki/Plenum_space
The idea is that if there's a fire, the burning cable could give off toxic fumes. If the cables are in a plenum space, the building's ventilation system could carry those toxic fumes to areas of the building which haven't yet been evacuated. The jacket on plenum cable is fire retardant to minimize this danger.