There's Virgin Mobile and Boost. Both are on the Sprint network. I plan to switch over to Virgin when my Verizon contract ends.
They do not have free phones though. You buy whatever phone that interests you, then pick a plan. On Virgin Mobile I think a $35 plan has 350 minutes and a $45 plan has 1200 minutes. The unlimited plan should be $55.
For "limited" plans, as long as you have at least 1 minute remaining for the month, you should have unlimited text and data for the remainder of the month. So if you have a 350 minute plan, you can talk your head off for 349 minutes on the 1st day of your month and continue to send/receive text and use data for the remainder of the month. Unless of course you use up that last minute.