Samsung SGH-U600 firmware update adventures - any advice?

[mystiky]

I was given a "unlocked" Samsung SGH-U600 phone by a friend. My carrier here in the USA is AT&T (Cingular). I have been using the phone for 2+ months and was experiencing some random "dropped calls" and "fade-outs".

As this phone is NOT sold or used by any carrier in the USA, I decided to see if maybe getting a "newer" firmware might fix the problem.

Looking at: http://frontside.be/word/2007/09/18/...u600-firmware/ as reference, the original revision that I had on this phone was:

U600BOGI1 (T-Mobile carrier code with a September 2007 rev. 1)

I then decided to "flash" this phone with OptiFlash to the "newest" version, which I could find:

U600XXGK2 ("Generic Western European" code with November 2007 rev. 2)

The flash went all okay, but when I restarted the phone, it would not accept any SIM cards. I tried 3 different cards, but I would still get an "Insert SIM card" message upon turning the phone on. However, when I tried to do the test codes on the phone, all was okay. And the diag code confirmed that the new firmware was indeed correctly flashed.

I then decided to "flash" the phone again to this revision:

U600BOGD4 (T-Mobile carried code with April 2007 rev 4.)

and now it is working again normally. I don't know if my problems have been fixed, as I have had this newer firmware for only 6 hours.
So, my question is this: Why would an UNLOCKED phone not work with that November 2007 revision? I assume that there is something still something in that phone which only allows it to work with a T-mobile related firmware. There are number of "T-mobile" only related options in this (& original) firmware (like Web'n'Walk , T-zones), and I would not mind loosing them since I use AT&T.

I am also wondering if the current firmware that I am using now from April 2007 revision 4 is "better" then what I had originally, which was September 2007 revision 1?

Any comments or suggestions are much appreciated!