If the GPS has responded to the SMS commands it's possible you may have entered the Apn incorrectly. Below is a list for Telstra, Optus and Vodafone apn commands for the Slim and Heavy Duty GPS Trackers


Telstra SMS GPS -  Apn123456 Telstra.Internet

Optus SMS GPS - Apn123456 connect

Vodafone SMS GPS - Apn123456 live.vodafone.com


The SMS Command should look like this (Optus APN Example)