While the iPhone was available from the four main U.S. carriers from 20th September,  those who want to stick with smaller regional carriers have so far had to wait. 1st October is now known to be the magic date for nine carriers, with others expected to announce shortly.

The nine companies who have so far announced that they will have both the iPhone 5s and 5c available from that date (via MacRumors) are:

Appalachian WirelessBluegrass CellularC SpireCellcomGCIMTANex-Tech WirelessNtelosStrata

Not all regional carriers yet support LTE for the iPhone. You can check which do in this Apple support document.