In response to the questions:
My co-workers phone did work just fine when we upgraded his phone immediately after mine. So to recap, when I updated my phone to 2.1 I had the phone reset issues, and his did not exhibit this problem, and his phone is still working fine.
Do the refurbished phones come with 2.1 already installed? So far the answer seems to be no, they do not come with 2.1, they come with the 1.5. Somebody earlier said that they can do it at the store (with Service Center) for you if you wish, but you would probably have to remind them since they didn't do that for me.
Note: It would be interesting for sprint to chime in at any time on this thread, since it's seems to have growing activity.
For the guy driving 1.5hrs, I will my earlier tip, make sure they have a Service Center (call ahead and ask). Print this thread, since it has plenty of info for the technicians to work off of.
It started rebooting again yesterday afternoon after few hours break. I was on a call to my brother who is in a flight traveling to another country for a month and I caught him a miniute before his flight leaves so that I can say good bye and then this phone reboots. By the time it finished rebooting and my brother's phone is switched off . I went to Sprint store and they spent an hour loading 2.1 and I know that will not change anything. They finaly told me that they need to order a phone for me. Not sure why they can't give me a phone that they already have in stock. They may have ordered a refurb for me which sucks. Anyone with this reboot issue quit trying to fix it on your own and get a replacement.
UPDATE: I got my 2nd replacement from Sprint on Saturday. This phone was much better than the last refurb I received (looked to be brand new) and I have not had any problems since the 2.1 update was installed on it. It's so nice to have a fully functional phone back.
I talked to the tech a little more about the situation that a few of us are experiencing and he still said that it really hadn't been addressed as a major issue yet.
I have been having this same problem and I'm going into the store today. The final straw after doing everything posted here to try and fix it myself, my 77 year old father got his leg crushed in a door, broke his fibula in 4 places and shattered his tibia and my phone rebooted in the middle of the emergency call. What is the point of having a cell phone if it can't be accessed in an emergency, I'm so angry and in hind site i wished i had never upgraded to 2.1. My husband and I got the same phone at the same time I upgraded he didn't, of course his phone is just fine. We got ours in Dec 2009 around the same time many people here who have complained.
Apparently, Sprint must be getting used to this problem. I called customer service about a month ago and explained my problem. I was then connected to Tech Support and talked to a level-headed guy. I explained the problem and what I had done to try to correct it (multiple installs, multiple hard resets, etc,). He decided that there wasn't any point in wasting my time or his and said he would send a replacement phone to my home. It arrived the next day, I moved my flash memory to it and fired it up. The latest version of firmware was already installed and I was able to restore all my data and apps fairly quickly (nothing like a little practice to make one proficient at anything). The phone (which was in excellent condition as was my old one) has worked flawlessly since, now entering its fourth week without a reboot. The replacement phone kit had a preaddressed, prepaid padded enveloped in which to return the old phone. The whole process was quick and painless and didn't require me to a) drive all over creation or b) waste my time doing again what I had already done several times. All in all, a very good job of customer support by Sprint.