Optus has apologized for yesterday's network blackout, the third in as many weeks, which silenced the carrier's voice services across Brisbane.

The failure occurred after a scheduled network performance upgrade went awry due to a glitch in a Nokia-issued software patch. Outbound voice calls on the Optus 3G network went dead from 6.30AM Wednesday until midday, but were terminated again in a separate, but related failure between 2.30PM and 6PM.

An Optus spokesperson would not comment on whether the company will pursue legal action against Nokia, or whether repairs to the upgrade will remain stable.

"We apologise to our customers for the inconvenience this has caused," the spokesperson said.

The outage comes days after the Optus 3G network was brought to its knees last Friday which knocked out voice and data services along the east coast.

Optus mobile and terrestrial communications services across Queensland were knocked out in mid July after council construction workers severed an interstate cable. A separate failure in an inland Point of Presence (PoP) exchange terminated services across the remaining areas of the state.