I can't make calls using a voice command

Try the following actions:

Verify that your BlackBerry smartphone is connected to the wireless network.
If you're using a Bluetooth enabled device, such as a hands-free car kit or wireless headset, verify that the Bluetooth enabled device supports this feature and that you have paired the Bluetooth enabled device with your BlackBerry smartphone.
Verify that your keyboard is unlocked.
Verify that the language that you use to say voice commands is the same as the voice dialing language that you have set in the language options. Certain languages might not be supported.