I have a Samsung Galaxy S4 (SAMSUNG-SGH-I337) which has been my phone with ATT until recently.
Build number: LRX22CI337UCUGOK2

Now it has become a legacy device and when booting it gives me this message:
SIM not provisioned MM#2
So, now I have to decide to find a new use for it or else to recycle it.

I've been looking into other firmware, but it appears that CyanogenMod will not work, since the phone has the wrong build number: http://wiki.cyanogenmod.org/w/Install_CM_for_jflteatt
This is the first time I may try to hack a phone and I'm indecisive, due to the possibility of bricking it.
On the other hand, I would like to give it some sensible use, since it is a fully working computer.

Hints will be appreciated.