So you thought to yourself, "I don't need to spend all that money on an iPhone 4; I'll be totally happy just getting the iPhone 3GS." Then you had a friend that got one, saw it, and instantly fell in love and cursed your wretched decision to save a few bucks, a few days, and not wait for the new one. Well you just may be in luck. You can either get some cash back for your purchase or turn your phone in for credit towards an iPhone 4.
Modmyi got a hold of a memo that states that anyone who purchased an iPhone 3GS between May 7th and June 7th 2010 can return their 3GS at the original price before the recent drop and get full credit towards an iPhone 4, of course paying the difference. Those who wish to keep their 3GS can get some cash back instead; May 7th-May 14th purchasers have to get their requests in by June 14th; after May 14th to June 7th have 30 days from their original purchase to get $50 back if they bought a 16gb 3GS, and $100 for for the 32gb version.
Those opting for the trade in for th iPhone 4 will have to pre-order it after turning in their 3GS from the original place of purchase, with their shiny new phones expected on June 21st.