Yes, you can. Lumin has a dial pad you can use to dial any phone number. Tap on Phone and then tap on the Dial Pad button located at the lower left side of the screen. Then use the dial pad as you would a normal phone.
You can also add new contacts if you want. Tap on Phone and then tap on +Add Someone, enter their name and phone number. Once this is done, you'll find this contact under Everyone.