4G service on month-to-month basis?

  I have a new religion when it comes to phones. I only do month-to-month, fully prepaid.
  If I want to switch, I don't have to call anyone and beg. I just forget to add more money to the account. Maybe I'll get a few emails reminding me I'm about to lose their service. But there's nothing they can do.
  Now with that in mind, I'm interested in knowing if anyone here has signed up for a 4G plan that is month-to-month and is happy with the service they're getting. Obviously I have a bias toward NYC, but I travel, so it matters how it works elswhere.
  I'm thinking of trying ClearWire. But I'm not sure if their service is any good. Hard to find much comment on blogs about it.