There is a plan called "seasonal Hold" for $15/mo.
But this will count as plan change. So when you came back from your vacation, you will have to pick a new plan which is offering at that time.
If you have a special promo plan or grandfathered/old plan, you won't get it back.
I wouldn't mind to pay my regular service charge if it's a month (or 2 even 3)vacation. Some promo/old plan is too valuable to loose.