We were given a brand new TELSTRA T-GATEWAY MODEM
have set it up via a wired connection -excellent
but can't seem to be able to set up wi-fi
book states -we should have a Network name and Key number -this was on a card when bought -but don't have it?
Anybody help?

B, October 2015

Can the person from whom you got the device help?

Seems to be a lot of support (and manual) here: https://crowdsupport.telstra.com.au/t5/Modems-Hardware/T-Gateway-User-Manual/td-p/92998

More general stuff here: https://crowdsupport.telstra.com.au/t5/Modems-Hardware/bd-p/Modems

You may get advice there how to do a factory reset

You could do well working out exactly which model you have.

XXXXX, October 2015