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Yes, the roaming charges will be very high even if you have a Roaming plan. Roaming plan is suitable only for a couple of days. Since your phone is CDMA, you may not be able to use the carriers in Asia because most of the networks are GSM.
So the best option is since you are staying for a month, buy a cheap GSM phone with tethering capability (you can get cheap smartphones with tethering capability for $50 or so). Then when you get to Asia, get a local SIM card from there and this will allow you to make calls and also, with tethering capability, you will be able to share internet to your main phone, computer etc with cheap plans of their network. Note : DO NOT buy CDMA phones. You will not be able to use these with GSM networks in Asia.
If you want to make US calles from Asia, then you can Skype as well
This is your best option. If you have any questions or would like any additional information, please don't hesitate to ask
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