I have unlocked my htc one xl recently from telstra network and put a optus sim card into my htc one xl, i am able to make and receive calls but my 3g wont work but did with telstra sim.
Try to put a other sim-card in it with a internet connection maybe it's just the provider that doesn't want you to use it.... If that doesn't work go to settings-connections-phone and then choose the 3g network