There are plenty of observers who wonder why Vodafone and Optus have held off for so long.
It was only ever going to be a matter of time before either Vodafone or Optus became sufficiently fed up with losing customers to Telstra that they would start a price-based war. And the battleground had to be data.
Optus has come out with its opening strike with demonstrably more attractive data deals and the industry is waiting to see whether Telstra and Vodafone will respond.
Customers are becoming increasingly immune to discounted offers on voice calls - a market that is clearly mature.
But those (which is almost all of us) that use smartphones are becoming voracious users of data and this is the service that will increasingly become the value differentiator between the mobile providers. There has been lots of tinkering over the past couple of years with data plans, but this week Optus set itself apart by offering a range of changes. It is a clear sign it wants to get back in the game.
Credit Suisse analyst Fraser McLeish reckons the Optus plans represent a structural pricing shift. That is a big call. He describes the new mobile pricing plans as aggressive - sufficiently so that Telstra will need to get in the game to defend market share.
On some of the bigger plans Optus will include unlimited calls and much more data. In addition customers will be able to share data across several devices for a flat fee of $5 per device. Telstra offers sharing but charges $10 per device a month.
The issue for Telstra is that to respond by offering more for the same dollar amount is the equivalent of reducing prices, which in turn cuts into revenue - a move it has largely avoided to date.
McLeish takes the view on how much it will need to respond and has reduced Telstra's mobile revenue growth forecasts in the 2015 financial year from 3.8 per cent to 2.1 per cent. Telstra has successfully traded as the premium network and due to the reach and reliability of its services has been able to charge higher prices. But over the past year main competitors Optus and Vodafone have been improving their networks and customer service.
To date Telstra has managed not just to keep them at bay, but to increase its market share and therefore revenue from the mobile division in what is essentially a mature market. If Telstra decides to deliver a competitive response to the Optus threat it will be game on in the mobile market - great for customers but not necessarily shareholders.
While for Vodafone and Optus a mobile war would need to be aggressive, Telstra will need to play defensively. (Its recent announcement on setting up free Wi-Fi hot spots for fixed broadband customers was a classic case of playing defensively in another part of its business.)
For these second and third-ranked market share players there is little point in tinkering with prices or services. They need to come out swinging. There are plenty of observers who wonder why Vodafone and Optus have held off for so long, given both are part of large, well-resourced international telecom companies.
Telstra CEO David Thodey has said in the past he was reluctant to engage in price wars, arguing Telstra's superior package involves a better network and service. And while Telstra is busy developing other parts of its business, the cash-generating mobile phone business will remain for a long while. It has long had a better coverage of 3G but its competitors are playing catch-up in 4G, another battleground.
Vodafone has for several years had a network disadvantage and the cheaper pricing to compensate but now says its network is back up to scratch - even though most consumers are probably unaware of it.
For Optus and Vodafone there is no point having large-scale investments in Australia and continuing to see their subscriber bases fall. Either was going to have to stage a comeback eventually. Telstra may take another leap forward next year when the 700 MHz kicks in, given it has twice as much as Optus and Vodafone none.