I need to be able to contact my office and my children while on vacay. My US cellular carrier wants 1.95usd/minute to phone home. Getting a JA phone is a "no brainer" for me.
If you don't need to call home at all, and don't have a lot of friends in JA to call, then a JA phone is not a requirement.
My JA phone cost me $12USD and the SIM card was $3USD. I call to the US for pennies a minute.