The point is that international roaming is generally expensive right now, the EU is now mandating a transitioning plan to free roaming with an intermediate rate cap which is most likely an improvement over existing EEA rates (my ISP's lowest EEA rate at the moment is 0.06€/MB)
Alas, you can't get a subscription as a foreigner (or at least, not easily). But you can get a relatively cheap, pre-paid SIM, which works just fine.
A lot of vendors at BKK (or any other airport) will be more than happy to sell them and configure your phone in the process.
They're also quite useful for reasonably priced phone calls home if you don't want to dicker with Skype and they can be topped up at just about every grocery store.
Anyway: Thank you for the tip. May it be useful to other travellers.