I’m not Australian, but I’ll give it a shot. In a nutshell - no 3G and no 4GX.
While the modem has the 3G frequencies you need it uses them for WCDMA. Telstra is a GSM carrier so that won’t work. The modem doesn’t get Band 28 (700MHz) so you won’t get 4GX, but that’s only available in major cities anyway so you shouldn’t miss it. Other 4G bands will work fine.