HTC One M8 for Windows - Manual (Page 103)

If you enabled your password but forgot it, you can still make an
emergency call without entering the password by tapping
emergency call on the lock screen and then dialing the local
emergency number.
Making an international call
1. On the Start screen, tap .
2. Tap to open the keypad.
3. Press and hold the 0 key until the + sign appears.
The plus sign (+) shows that you're making an international call
(instead of entering the international access number for the country
you're in).
4. Enter the following on the keypad:
§ Country or region code
§ Area code (without the 0 at the beginning)
§ Phone number
5. Tap call.
Phone calls 103