Telecom competitors Vodafone and Optus have agreed to a joint venture project to build 500 more new mobile phone stations in the next four years to address network problems.

Vodafone, the third largest telco in Australia, launched on Friday the expanded network JV which would grant Vodafone access to 400 base station sites of Optus, the second largest telco in Australia.

The joint force would mean the two firms would challenge the supremacy of number one Australian telco, Telstra, which already has fast 4G mobile services available for clients. The joint venture will need the approval of the Australian Competition and Consumer Commission.

Vodafone Chief Executive Bill Morrow said the joint venture is proof that telcos are responding to customer demand for better, faster and more reliable network across Australia.

"The expansion to our coverage is a significant step forward and is part of our evolution toward higher performance network speeds that will ultimately lead to our introduction of 4G," Mr Morrow said.

It would also mean faster delivery of improved 3G and new 4G services for Optus clients, said Optus Chief Executive of Consumer Kevin Russell. He said the construction of new sites would mean a 20 per cent improvement in number of mobile sites on the Optus mobile network in the next three years and cost reduction for both companies as they share the cost of expanding their mobile infrastructure.

For Vodafone, the JV would increase its sites to 1,800 which include the 500 news ones to be built, and access to 400 of Optus sites and 900 from the 3 mobile network which was the result of the June 2009 merger of Vodafone and 3, and would lead to the demise of the 3 brand.

Disenchantment with the telcos' services has caused more than half a million customers to transfer to rival telecommunications firms in 2011.

To address customer dissatisfaction, besides the JV with Optus, Vodafone has spent $1 billion in the past four years to put in place 1,100 new 3G sites, with 400 more sites expected to be finished and operational within months.