Telstra and Optus have declined to delay the impending shutdown of their 3G mobile networks, despite a Senate inquiry cautioning them that the move could jeopardize public safety. Telstra, Optus, and TPG/Vodafone are shutting down their aging networks in August, September, and January, respectively. However, the Senate inquiry warned them the shutdown could cause widespread disruption to essential services and infrastructure, such as critical medical equipment, fire alarms, EFTPOS machines and waste and water infrastructure, the Australian Associated Press reported. Over 200,000 Telstra customers risk being left without mobile service after the 3G network shuts down due to using outdated phones. While some older 4G phones might also be affected, the real worry was that the subset configured to default to 3G for emergency calls leaves users unaware of the issue until it's too late. The committee also suggested placing conditions on Telstra and Optus if they decline to postpone the 3G shutdown.