I would suggest you contact your carrier (Movistar) as the Vodafone VF685 supports 850 900 1800 1900 GSM frequencies (and both South Africa and Argentina shares the 1800 frequency band.
Edit: According to the GSM frequencies map here, Argentina only supports 1900 and 850 - non of which is supported by South Africa (SA takes 1800 and 900). According to the same map, SA and Argentina does not share any GSM frequency band and hence the Vodacom Smart Kicka (a.k.a VF685) will not work in Argentina :(