How to unlock sch r351

Hello,
help me....
i have an old samsung sch r351 (samsung pinger called)since jan 2010 injected smart telekom (cdma 1900).
at this time i must go out from jakarta to kebumen (obout 350 miles) for a job, and i can't use my samsung becouse here is outoff smart telekom coverage.
and i can't inject other number operator to this phone, becouse locked by smart telekom.
question ....what can i do?, here is no samsung service center.
help me how to unlock this samsung, i want to inject fleksi (cdma 800)