It's a cheap, low-end, no-name Chinese Android, a ZTE v768. You know, an example of the type of phone that Apple should make in order to rebuild its marketshare. Cost me US$50, and that was far too bloody much. Perhaps an expensive name-brand phone would be better, but I've cruised the various fora of several Android vendors (including, of course, Samsung) and have noted that a _lot_ of Android phones seem to freeze for no reason. Indeed, the very fact that there is a special way to unfreeze the things says quite a bit.
Basically, T-mobile support says (and numerous fora confirm) that when Android phones in general and my phone in particular run low on available RAM, they freeze. When they run low on space on their SSDs, they freeze. My phone is low on both RAM and storage, 'cause it's an older, cheaper, phone (it only runs Gingerbread and cannot be updated 'cause it doesn't have the RAM or storage, or, indeed, CPU, required) and unless I do things like clear files, down to logs, out of the storage and reboot the phone every ever so often, it'll freeze. It'll even tell me that it's going to freeze: I'll hear the little TM boing, and when I look at the phone it'll be rebooting spontaneously. Once it boots, I can't do anything with it. I can't get to the main screen. I can't send or receive calls. I can't do anything except pull the battery. Once I pull the battery and replace it, the phone works again. Until the next time.
I've seen reports of brand-new phones, such as S5s, doing the same thing. (See http://forums.androidcentral.com/samsung-galaxy-s5/379912-s5-freezing-up.html, for example; note that that thread's been going on for _months_ and mentions numerous Samsung devices, all new, all doing the same thing) I really don't see any reason to pay a lot of money for a major brand Android and have the same problems again. I really don't.
Sorry if this offends the local fandroids, but that's how it is. The Android doesn't work properly. It just doesn't. The iPhone does. As a direct result of my bad experiences with the Android (and my checking around to see if I was alone; I wasn't) I won't be chancing another Android. It's that simple.