I don't know/remember what the SIM/ESN situation is going to be once Verizon completes their total LTE rollout. At first I do remember reading that LTE was going to be SIM based, but more recent articles have still sqpoken about ESNID so I'm not sure.
Basically, Sprint and Verizon do not use SIMs unless they give you one with a World phone; AT&T and T-Mobile, both being GSM carriers, do use SIMs.