I'm picking up iphone 4 on cl at 300 sometimes less all day long, sure there are sellers that still live in denial where they still want 350 or even 400 but oh wells they just sit on them for weeks then ending up with a price drop.
Iphone 4s/5 won't make the price drop overnight since the supply won't meet the demands for the earlier month, it is all a gamble since you don't know how ground breaking the new device will be, if it's a small upgrade the value will hold well, however if it's like ipad 1 to ipad 2 then the values will plumet for the iphone 4. I don't think we are talking a huge drop since most of the time you will sell your phone by pricing it $20 below the moving average.