Generally when Apple releases a new model of iPhone they keeps the current iPhone model on the market at a reduced price. So during the launch event of iPhone 5, Apple might announce White iPhone 4 at a reduced price.
Also Apple is going to organize this year’s WWDC based on the “Corporate Meeting” placeholder in the official Moscone center between 5th and 9th June. During this period Apple might release iPhone 5. Well, From the above informations it is expected that definitely Apple will release iPhone 5 before 20th June.