Assuming the iphone 4s doesn't suffer from this issue, the decent thing to do would be to swap like for like, then refurb the old 4 series to a usable state and rebrand it.
or, you could piss off customers even more with a derisory $15 that will be tied up in so much shit, you won't bother (or bother to get another iphone/apple product).
Not being funny, but if I was to ever overpay for a product on the scale of Apple, i'd want top notch customer service.
Summary: If Apple ship crap, you're on your own pal.