Telstra was amongst the carrier partners specifically named by Mozilla as part of its Global rollout of Firefox OS. From Telstra's side, however, it appears that it's simply testing the Firefox OS waters.
Given how sparse the Telstra quotes were in this morning's announcement, I checked with Telstra locally for comment on Firefox OS. Here's the statement I was sent:
We welcome new entrants to the mobile OS market - ultimately it means more choice for consumers. At this stage we're yet to decide whether we will offer Firefox OS mobiles. We'll be evaluating phones running the OS in the coming months. One of the potential advantages of Firefox OS is that it could help bring smartphone features to lower-cost devices.
Or in other words, somewhere in Telstra's test labs there sits a lonely Firefox OS phone, and it may be the only one Telstra ever has, or alternatively, by this time next year we could all be chin-deep in Firefox OS phones.