Voice cabling (sometimes referred to as Cat 3) allows cabinets and telecom distribution points to interconnect throughout your sites infrastructure. Traditionally this type of cabling was very common especially when structured cabling was introduced.
These days with the introduction of VoIP, voice cabling has taken more of a back seat as VoIP can be run over traditional data cables like Cat6 and fibre links. Some older systems depend on their voice infrastructure to support their telephone systems demands and this type of cabling is common in many sites.