Edit in JSFiddle

var ContactModel = Backbone.Model.extend({ //extend Backbone.Model
    getFullName:function(){
        return this.get('firstName') +' '+ this.get('lastName');
    }
});

var contact1Model = new ContactModel( //instantiate ContactModel instance
    {firstName:'John',lastName:'Doe',phone:'111-111-1111'}
);

var contact2Model = new ContactModel( //instantiate ContactModel instance
    {firstName:'Jane',lastName:'Doe',phone:'222-222-2222'}
);

//call the getFullName method on our models
console.log(contact1Model.getFullName()); //logs John Doe
console.log(contact2Model.getFullName()); //logs Jane Doe