I would like to make ATT prepaid temporary suspending

What you need to do before you leave is log into your account, change to a pay per use plan and refill your account with $100. A $100 refill is good for a year and will still be there to use when you return. When you return, just change back to a monthly plan.

Thanks for answering. My current plan is $35 per month. I checked on ATT prepaid plan and there is a "25 cent per minute" plan. For this "25 cent per minute plan", is that mean if I don't use it will not charge? SO I can switch to this plan before I leave? And I can switch back after I back to US?

Best regards,

For this "25 cent per minute plan", is that mean if I don't use it will not charge? SO I can switch to this plan before I leave? And I can switch back after I back to US?

Yes to all, provided the $35 plan still exists. ATT does often change their plans.