Iphone 4S CDMA phone, Can it be used in a GSM netwok??

Hi everyone,

I have a iPhone 4S, locked to Japan AU network. I think this is a CDMA phone since it has a IMEI starting from 9900.............

But it's Model is A1387. I'm a bit confused about this & I want to know if this can be used in a GSM network if I get it unlocked.

It has a SIM slot, I searched everywhere but couldn't get a trustful answer for my question.

Appreciate it verymuch if someone would help me on this matter.

Thank You