some are....some aren't. here's the options for basic phones:
all of the used devices are certified preowned devices.....and it will state if it is a certified preowned. if it doesn't say that, then it's new (fyi.....i've bought cpo's before and there was no way on earth to tell that they were not brand new)
I've always bought CPO phones when they are cheaper for the model I want. I've never had any more issues with a CPO phone than i've had with a new phone. As AZ said, if it didn't have the sticker on it when you bought it you wouldn't know it was CPO.
I, too, have purchased CPO devices and have been very satisfied - no issues, phones behaved as if they were brand new. I wouldn't think twice about buying another CPO - $$'s less for a slightly used, thoroughly tested device is a good deal, IMHO.