Kutster, I hate to correct you but I actually did successfully connect my Droid DNA using the Walmart SIM card. Now in my area it was actually called FamilyMobile, and run by T-Mobile. I purchased a SIM card from Walmart, took it home, plugged it in, set up an account, and it worked. Granted, you don't get LTE, but it does work and is mega cheap ($40/mo unlimited). I ended up cancelling and taking it back, simply because the internet was very slow, and the coverage wasn't very good in my area (T-Mobile sucks in my area). I do want to stress though that it definitely does work! I think I'll try AT&T GoPhone next.
The important thing to remember is this phone (the DNA) has all the radios necessary to connect to just about anybody but Sprint's network. Don't always believe what the companies tell ya.