Short codes don't work because the phone number they give you is classified as residential, not mobile.
I use Republic Wireless and I like it. I'm not in love with it though, mainly because I think the Moto X was overpriced ($300) for what it delivered.
It is cheaper than a flip phone though, and I've gotten a few referral credits (which, btw, I can hand out to anyone interested, it's $20 off).
The most annoying surprise you will get is how much taxes add on to the cost. I stay on the $10 plan most of the time and taxes add 37% to the cost of the plan. Three bucks and seventy cents.
I probably would not get the Moto X if I were a new customer. I would get the Moto G, which IMO has 90% of the functionality of a Moto X for half the cost.
Oh, and service. For a while the wifi to cell handoff was way too aggressive. Supposedly they have fixed this in a recent update. Generally wifi calls sound great and cell calls are lousy because of sprint. Battery life of the Moto X kind of stinks also. I still carry two devices with me: the Moto X and an ipod touch for music and other stuff, because the Moto X would quickly run out of power if I used it for music listening as well.
If the X had an SD card slot I would like it a lot more. 16gb is just too small.