The activation is simple. Just SMS the plan you want to 888. For example, "DT20" SMS to 888. If you didn't select, the stored value will be used to deduct the data you used in per kb. And they keep changing the plans. At first, i used D5. Later they said my type of cannot use D5, can use D7. This trip, new pattern come out. Say D7 is promotional and I disabled it last trip, and i can use DT20 for 2gb , 10k VND per day. I don't think i can use 2gb each day, especially it's just 3g. So i opt for DT20 which is 20k VND per week for 1gb data.
Unless you intend to sit in the park the whole day to surf the net, you don't need 2gb especially it's the slow 3g speed. Every shop and hotel there have wifi, and it's quite fast. At least 30Mbps speed. So no need to be scared and buy so much data. You wont need it.
Oh ya, if you have problems with the sim card, you can call Vinaphone customer service at 9192. They can speak english and Mandarin.