This really isn't that accurate anymore. Verizon Wireless, which is the largest carrier in the US right now, uses sim cards in all of their LTE devices. Behind them is AT&T which of course is completely GSM and T-Mobile. Sprint, well... they're there.

Sprint phones also use SIM cards too, for their newer LTE devices.

Some LTE devices have embedded SIM cards (baked inside the device so they aren't user removable, such as the Photon Q LTE).

But those are still SIM cards, all Sprint LTE devices have a SIM card of some sort.

Correct me if I'm wrong, but I don't think most people have an LTE phone.

Given that people typically get a "free" phone every two years, I'd imagine that most people in the US have LTE phones by now.

Well, most people out of the 56% that actually own a smart phone: http://www.pewinternet.org/2013/06/05/smartphone-ownership-2...

Is LTE only used for data, or is it also used for normal voice calls?

Most people have a GSM or LTE phone.