In order to make a call from your Firefox OS phone you have to tap the Phone application on your Home or All apps screen.
You will see 3 different options you can use to place a call:
1. The Dialer button allows you to manually dial a number by using the keypad.
After you finish entering the number, tap the
button to place the call.
Tip: To dial internationally, tap and hold the 0. To dial voicemail, tap and hold the 1.
If you entered a wrong number, erase it by using the
2. The Call log screen sums up all the incoming, outgoing and missed calls. You can call back directly by tapping on a number.
3. The Contacts tab shows you the contacts you most called on top of your list followed by all the other contacts. Tap on any of them to make a call.
4. To end a call, tap the red hang-up button.
If you want to place an international call, make sure you check with your carrier for international rates and roaming charges. You may also want to check the international dialing code as well as the area dialing code to place the call properly.