Telstra will invest an extra $500 million in its mobile and the national broadband (NBN) transition networks over the next two years, the telco says.

Telstra said the investment of $500 million of excess cash would “maintain and extend our network advantage” in mobile and “bring forward benefits from the NBN agreements”.

Telstra, which on Thursday reported a 2011/12 full year net profit after tax of $3.4 billion, added 1.6 million domestic mobile customers in the period, taking customer numbers to 13.8 million.

The company’s chief financial officer, Andy Penn, on Thursday told AAP he could not provide forecasts on whether the same level of customer growth would be maintained in the 2013 financial year.

“Our focus is to continue to invest in the quality of the network,” Mr Penn said.

Telsta said it was not considering capital management initiatives at present.