Apple iPhone 3G has been a superhit globally. And with the rising expectation from the next gen iPhones which is expected to be out latest by July 09; the sales of the current iPhone 3G can take a hit.
Typically before, Apple launches any new model the old ones are kept in supply such that they are sold out at least a few weeks before the new model. It is rumored that preparing for the new iPhone(s) T-Mobile has dropped the price of iPhone 3G in Germany, and O2 of the United Kingdom is considering the same (in May).
Next weeks Apple event might not reveal in detail about the strategy with iPhone hardware. But software would give enough juice.