I was hoping to find out if I can use my 10.1 inch Android tablet running Android 4.1 for calls and texts using a SIM card attached through mini USB (or if not, how?) Surely there must be a way.
I think what you're looking for is a full-blown 3G USB dongle, not just a SIM card adapter. See, for example: Can I receive/send SMS of cell phone number with a tablet using dongle?
A SIM card adapter would simply be a device that can read the contents of the SIM card and possibly edit it. So it's pretty much like an SD card reader. To send and receive text messages and voice calls, you still need a transmitter, which is what a USB 3G dongle will provide (if your tablet doesn't have built-in 3G support). However, I'm not sure if you can use a 3G dongle to make voice calls, although SMS is pretty much a standard feature for such devices.
I have a Freelander 9.3" tablet with sim slot. I have used it to call as long as I have a bluetooth headset. Got it from China, but the vendor doesn't carry it any more see item # CVAGW-104152. It works great if you need to use your computer AND make a call too. It is quite handy, but not pocket worthy... Wished I could get a newer version for my wife.