This read-only integer reports the cumulative time, in seconds, that this port has spent on voice calls specifically, as distinct from fax or data usage on the same channel. Admins use it to see the traffic-type breakdown for a given port, useful on gateways that carry mixed voice/fax/data traffic over the same physical channels. For example, a port showing high totalVoiceUsage and near-zero totalFaxUsage confirms it's effectively being used as a pure voice trunk in practice, even if it's technically capable of carrying fax.