This (evidently) is a genuine Telstra number but beware if you get a call, ostensibly from this number, and the person calling claims to be a Telstra technician and asks for personal or sensitive information, or attempts to acquire access to your computer, or asks you to check the ID on your computer.

It could be that the number appearing on your phone is not the true number of the phone from which the call originates, and the call is almost certainly a scam. If in doubt, check with Telstra.