Meh, I was a smart-alec kid there with my friend. The salesperson had to go get a sim card "for the LTE to work" and I said "oh right, because LTE is GSM and requires a sim". The salesman insisted Sprint didn't use GSM so I looked up the wikipedia page for LTE on one of their demo phones and started reading out loud "In telecommunications, long-term evolution (LTE) is a standard for wireless broadband communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA standards."
That's when the salesman told me to leave.