HTC One Remix - Manual (Page 129)

4. Tap the contact you want to call.
If you selected a contact whose phone number has a leading zero,
HTC One remix will automatically prepend it with your home
country code when dialing. If there's already a plus (+) sign and
country code before the phone number, HTC One remix will just
dial as is.
HTC One remix dials as is and does not prepend your home
country code when you call phone numbers that are not stored in
HTC One remix. When manually entering a phone number to call,
you need to enter a plus (+) sign and country code before the
number.
Editing a country’s international call settings
1. Go to Settings, and then tap Call.
2. Tap Assisted Dialing > Reference Country.
3. Under Reference Country, select the country whose settings you
want to edit.
4. Tap > Edit.
5. Edit the Country Code, IDD Prefix (International Direct Dial), NDD
Prefix (National Direct Dial), Area/City Code and National Number
Length (length of phone number).
6. Tap Save.
7. Tap Done.
Phone calls 129