It'll be a refurb. It's very rare that they have you a brand new phone unless you've repeatedly had problems with the refurbs. It's extremely unlikely that you'll have an issue with the refurb though as they are very stringent in their refurbishing process. Each refurb gets a new front, back, steel band, and battery.
http://store.apple.com/Catalog/US/Images/apple_certified.html
Although now that I think about it, Apple's in-store replacements could very well be refurbished models that have a cosmetic blemish, like the ones sold via AT&T's website.
If the replacement phones are refurbs, then how were there 4S replacement phones in the black boxes on 4S launch day?
Service replacements are NOT refurbs.
If the replacement phones are refurbs, then how were there 4S replacement phones in the black boxes on 4S launch day?
Service replacements are NOT refurbs.
Call that whatever you want, but its not fit to call it refurbished. Refurbished means that the entire device was owned by someone else before you basically, and the service replacement phones do not fit this guideline.
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Wrong. There are no refurbishing guidelines or standards or definition that all companies follow.
Never said all companies follow anything... just what Apple's standards are.