[Update posted July 30] : The HTC Touch Diamond is currently exclusive to Telstra. So while the handsets we are currently selling are unlocked, they have been pre-configured for use on the Telstra network and contain Telstra settings, start-up/shut-down logo and have a very small Telstra logo on the rear battery cover.
To use with non-Telstra networks, the device will auto-configure when the network is detected.
This is the 850MHz version that runs on Telstra NextG, and it also runs on Optus/Vodafone 3G networks (2100MHz). It is quad-band GSM as well so can be used on any GSM network.
The non-Telstra release of the HTC Touch Diamond in Australia is not scheduled until at least October - possibly later.