Ultra Mobile is a Mobile Virtual Network Operator owned by T-Mobile that has a market focus on international text and talk calling plans. An MVNO is a cellular service provider that does not own the wireless network infrastructure that is used to provide service.
Ultra Mobile does not sell cell phones, they sell SIM starter kits that allow a user to convert any unlocked Android or iPhone to his service. Ultra Mobile offers several calling plans that include unlimited international text worldwide and unlimited international talk to a specified list of countries. Some plans include additional worldwide international minutes, or dollar credits toward minutes, for calls to countries not on the specified list.