Regarding setting up your account into Zoiper for iOS, follow these steps:
1) Start Zoiper and go to its "Settings" tab.
2) Open the "Accounts" section and select the "+" button into the upper right corner.
3) Select whether you you already have an account or not;
4) Select whether you will manually configure your account or you will select your provider from the list;
5) Choose the type of the account - SIP or IAX.
6) In case you are configuring your account manually, enter the information you receive from your VoIP provider about Domain, Username, Password, etc. into the appropriate fields and select the "Register" button.