//load a sale by ID 
var sale = PublicAPI.CRM.Sale.Load(3);

//create a call 
var myCall = PublicAPI.CRM.Relationship.CreateCall(sale);

//myCall - created call for a sale sale 

//WARNING!! A call is created without a name. For correct work with the call, you should 
//specify its name and sabe the object to the database
myCall.Theme = "Call Name";
myCall.Save();