There is a DTAC store in the building just on the far side of the JW Marriott and another recessed into the East entrance into Robinson. You can add to your DTAC card and keep the same phone number if you get back before it expires. You can add in 800 THB increment (or less) and each time you add value you also add 3 months until expiration. You can "stack" your purchases until you have 1 year until expiration, or you use the value, whichever comes first.
