No, we don't know why, because you gave no details
1 - are the APNs configured properly?
2 - is the phone set to WCDMA, or WCDMA/GSM, or just GSM?
3 - does it work on EDGE, just not 3G?
4 - does it actually connect to Telstra (for voice/sms) ?
5 - is it unlocked? or are you using a hypersim?
it's unlocked and i've used it for a few calls and quite a few sms
"Unlocked" usually doesn't really mean a whole lot these days when it comes to getting mobile internet working on a mobile handset. Even the other "unlocked" devices still require some type of APN settings to be input. Just sayin'