They don't give you a phone. I always have an extra phone myself. If nothing else, you can get a $10 dumb phone and activate it with your number while your phone is gone, if you don't have another.
Taking the OS off and putting it back on, can do wonders, it will correct things that no number of reflashes or resets will do.
In Plano and in Los Angeles, they have walk in locations, those might can be done while you wait or that day. They are planning on having more walk in locations around the country and they can't remove the OS at Best Buy.
It takes 7-10 days for you to get your phone back.