Can I use my ATT iPhone 5S for any other Verizon, Sprint etc? Any others?

Can I use my ATT iPhone 5S for any other Verizon, Sprint etc? Any others?
I got disconnected from ATT, can't pay the bill. Can I use the phone for any other carriers?

There are theory's that you just need to get a different SD card suitable for the wanted carrier, there's a small slot of the right thing side if facing the screen and you just need a special tool to open that which you should be able to order from online, but the SD card may not be cheap, I suggest looking into this more before trying it.

NO, once your phone is blacklisted (blocked) by AT&T you can't ever use it as a phone again on any carrier.

Nope AT&T will blacklist the phone for a nonpayment on the bill and the phone will be very useless

AT&T is GSM and Verizon / Sprint are CDMA. They're incompatible. But you can unblock and unlock the phone and use it on StraightTalk or MetroPCS or SimpleMobile. If you need help with getting the phone unlocked and unblocked, mail me for references/