I've heard of Ting. It runs on Sprints network so the phone may only work with sprint.
The HTC one Sprint sells has an unlocked aim if I'm not mistaken so...
From what I saw online it seems like the sim is only unlocked for international use. http://forums.androidcentral.com/htc-one/267640-yes-sprint-htc-one-has-sim-card-yes-its-global-roamer-2.html