A typical smartphone costs around $200, but it’s usually shackled to a two-year contract that often costs $70 or more monthly and includes limits on data consumption, voice minutes and texts. Even prepaid smartphones, without a contract, can cost $30 to $50 a month and carry limits. But I’ve been testing an Android smartphone from an upstart carrier that charges just $19 a month for unlimited data, voice and texts — with no contract. That’s right: $19 a month, unlimited. This carrier is called Republic Wireless, a private firm in Raleigh, N.C., which launched its service in December. The sole phone that works with the company’s technology is a Motorola model, the Defy XT. The phone costs $249 — partly to help offset the low monthly price. However, as of Tuesday, the company is offering a second pricing option for people who would rather pay less up front.