While other carriers, including AT&T, have MyFaves-style uncapped calling to pre-selected phones on any network, Sprint only had unlimited Sprint-to-Sprint calls—until now. Any Mobile is for "Everything Data" plans $69 and up, but there may be roaming implications…
Adam Fendelman over at About has dug into the fine print, and says that unlimited minutes must be while on Sprint network, that is, not while roaming. Sprint also lists the following usage limitations:
Sprint may terminate service if (1) more than 800 minutes, (2) a majority of minutes or (3) a majority of kilobytes in a given month are used while roaming.