3G services provide higher bandwidth to mobile devices, allowing services such as video calling and mobile broadband.
The two carriers share a 3G network which had previously only been available in Sydney, Melbourne and Canberra, in addition to the airports of Brisbane, Adelaide and Perth.
"Customers in Brisbane and the Gold Coast central business district will be able to enjoy Optus's 3G products and services from April 1, 2006," Optus said in a statement.
A Vodafone spokesperson confirmed the carrier was planning on releasing a statement about the extended service later today. The company originally revealed its expansion plans in the middle of last year. Optus today said it would "continue to roll out the 3G network to Adelaide and Perth by mid-2007".
The other national 3G network is shared by Telstra and Hutchison.