From what I asked in Bluecube, 3GB Data +3GB Wifi promotion registration should be until end of this month..and the package(3GB Data +3GB Wifi) is valid for 6 months.. 

After that this plan will back to 2GB.. 

I called to Celcom Customer Service just now to enquiry about the First Basic 38 3GB data promotion. The CS confirmed we will always have 3GB month as long as we keep the line active.