Zoiper can work anywhere in the world as long as your country does not block VoIP.
However, to use Zoiper you would need to register with a VoIP service provider. You will receive your phone number (SIP account) from them which you can set into Zoiper. Pretty much the same way as when you purchase new mobile phone, to make calls you also need a SIM card. Imagine your SIP account as being your "SIM" card. : )
Ask your ISP if they can recommend any VoIP service providers in your area.