Telecom is forecasting its profit could fall by up to 26% in the 12 months to June next year, as it comes up against increasing competition.
Investors in Sydney on Thursday were told it expects to post a profit of between $370 - $410 million.
That compares to the $460 - $500 million profit it expects to report for the year to June this year.
Capital spending will peak at $1.3 billion in the current financial year, easing to $750 million in 2013.
Telecom expects that investment to start paying off by 2011, with strong growht in operating returns.
The company is due to launch a new 3G mobile network on Friday.