Freezing is NOT a common problem on these phones. It's possible yours is defective, but much more likely a software, media file or SD card issue. Since all you've done is vent, I have no way of knowing what you might have already tried in the way of fixing the problem, but since you appear to have little patience I'll suggest the following:
1. Back up any important data you have on the phone, ideally to a PC or other device, not the phone itself. Use Kies, or Helium Backup from the play store.
2. If you have one installed, remove the micro SD card. Make sure to unmount it or shut the phone off, first.
3. Factory reset.
Do NOT reinstall all your 3rd party software. Use the phone factory fresh for a few days. If it still locks up, with no 3rd party software and no SD card, your phone is defective, and needs a warranty repair. If it works fine, the problem isn't the phone.
Reinstall the SD card. If the problems recur, you have a bad card, a corrupt directory on the card, or corrupted file(s). Reformat it in the phone. If that doesn't fix it, buy a new card. If it does, start copying files back, but note that if you copy a corrupt media file back the problem could recur.
If the SD card doesn't cause the problem, start reinstalling your apps, a couple at a time. If / when the phone start misbehaving again, you'll know it's one of the recently installed apps.
@meyerweb, I am based in Kenya, E Africa and my S3 (i9300) has been misbehaving (freezing every few minutes) in the last 2-months or so. Now that I think about it, it may have started this behaviour ever since I mounted an external microSD card.
Basically what happens is that I receive a phone call and as soon as I'm done, it freezes. Similarly, when I connect to the bluetooth in the car, inevitably when I leave the car the phone freezes. In addition, I've noticed that WiFi doesn't always connect - it indicates that there's an authentication error - and soon after that problem, the phone freezes. However, these aren't the only instances - it might be charging in the morning and when I go to disconnect it from the charger, it won't turn on. Also if it is just laying on my desk in the office, I pick it up to do something and it's frozen. Sometimes it freezes when it's starting up, and won't display the phone lock-screen. Other times it will freeze and when restarted it will work for a few seconds and then freeze on the operation I'm attempting - like if I'm trying to make a call.
When I say frozen, what I mean is that when the screen is off, it doesn't respond to anything - buttons, etc. If it freezes when the screen is on and I'm using it, it won't respond to buttons being pressed, or swipes of the screen, etc. Sometimes, it's only seldom that this happens, the in-built back and menu buttons might light up, but that won't mean that the phone will unfreeze. If it freezes when the screen is on, the freeze will result in the screen not changing at all - it will remain that way until I either remove the battery, or press the start (on/off) button for about 10 seconds.
I thought it was the stock Samsung Jelly Bean version (4.1.2), so I rooted my phone and upgraded to AOKP Jelly bean (4.2.2). It was initially fine for a few days, but then the problem recurred. I had read somewhere that the Samsung -XELLA update was the culprit and that's why I rooted and upgraded. I also read that the problem is with the flash memory on the motherboard that Samsung made some S3 phones with. Are either of those likely to be the problem?
I've tried clearing the cache and Dalvik cache but that doesn't solve the problem. My wife has the same phone (different colour), and way more apps on her phone (she lets the kids use hers to play games, etc), but she hasn't experienced ANY of the symptoms that my phone has exhibited. My brother has the exact same phone but hasn't experienced any of the problems either. My phone's protected by Lookout Security Anti-virus - would that catch all viruses?
I'm following your advice - I just removed the external SD card... from your directions above, should I / is it possible to unmount the internal card? Immediately, it appears that the phone isn't freezing as much, but I suppose only time will tell. As I was writing this, the phone froze again (so perhaps it's not the SD card) so I'll try to wipe the phone and start loading apps one-by-one and see if I can isolate the problem to an app...
Any advice you can provide will be highly appreciated.