Changing Contacts telephone number format

Hi all. I bought an iphone 6 in USA and I am from Argentina. In the apple store (USA) the product was activated.

Do you know how can I change the Contacts' phone numbers' format so as to avoid the use of brackets () ?

I already selected the propper language for me (spanish) and the Region (Argentina) but the formats remain unchanged.

I still haven't placed a SIM into the iphone because I have to ask the carrier for a Nano-SIM which I do not have at the moment. May this be the problem? When I insert the new SIM I will have the right formats?

Thanxs!

Juan