Aw man, could've used this info about a month ago before I left for the states.
Nonetheless, good to know and this should definitely be included in one of those pinned posts Hannes!
1300NT is about the price for that plan if you buy from the TMO store in the states.
I'm curious, if it's an official T-mobile SIM card, how could it take 3 days to activate? Or do you mean UP TO 3 days?
In my experience, when I landed in SFO (from TPE), I plugged in the SIM card and called the 800 number on the back. After going through the processes to activate the card, customer service said it would take up to 3 hours to activate, but it only took 5 mins.