Prepaid SIM card: How do credits for voice and data services relate to each other?

[Tercera_Edad]

This thread is probably only for those in a similar situation, not least because a meaningful exchange quite likely requires some degree of knowledge or personal experience in this field, something that others will hardly have. And yes, as my ID insinuates, I'm not a member of some contempo influencer, selfie or likewise generation - which should not be mistaken as an assumption of 'ignorance, old fashion' and what have you; more like a different thinking, and maybe not inferior to what has become to be considered as 'modern'

 

 

--> All the following information stated according to best knowledge

 

When the precursor of today's digital mobile telephony appeared in the late 80s, the european-designed 2G/GSM standard, also prepaid cards were introduced; before that, only payment via credit was available. A usual method (thus not the only one) was to virtually deposit one's credit card in the provider's system; then you could transfer more airtime from the credit card to one's phone account, to which the SIM card was linked.

 

These operations were carried out (and still are) through USSD
https://en.wikipedia.org/wiki/Unstructured_Supplementary_Service_Data
Fx, checking one's balance was done by typing *121# then sending it; a moment later, the balance appeared on the screen.
(Providers are free to establish USSD codes themselves, they can therefore vary among providers.)
If you wanted more funds to make calls, like 20 'rubles', you would type *137*20# then send; a moment later, your topped-up balance was shown. This was in the era prior to packet-switched data, ie also data calls (internet) were treated like voice calls - by duration not data volume.

 

All this was a convenient system, not least because all that was needed to execute this business was mobile coverage, not an internet connection, nor some 'app'. Reason enough for me to stick with it, instead of thoughtlessly jumping on the manic-raging american 'innovation' bandwaggon, just because 'everyone else' does it.

 

Around the mid-90s, 3G/UMTS started to appear, and with it data packet switching ('always on') that offered charging data consumption by volume, rather than duration. Also, simultaneous voice calls and internet surfing became possible. It was also the time when special data tariffs were introduced. But you were free to just use your existing pre-paid balance also for data, if you so wished - no need to have a designated balance ear-marked for data usage.

 

Of course, I also have a laptop, and I usually use it via wifi. If there's no wifi and there's an 'urgent' need for internet access, then I connect the laptop to the mobile network via my 4G phone's modem - a process called tethering. The link between laptop and phone is established by wire (USB), or if without, then through Bluetooth or a kind of wifi. This situation doesn't arise very often, so until now I have felt no need to better understand how the prepaid systems for voice and data relate to each other in necessary detail. It would also be hard to find out here; even if one happens to speak sufficient thai, one would have to find an expert able and willing to explain how this is set up - good luck with that!

 

Presently, when my wifi is down (happens occasionally), then I just access the web via tethering. This works fine for the first five minutes, but then I receive a text from AIS on my phone telling me that for continued speed, I must buy a data package that costs 'so much' and will last 'so long'. If I ignore that and continue on my existing balance, speed will be throttled (it's still usable but feels less comfortable), theoretically until my balance has been consumed.

 

So I'm actually considering now to get such a data package, for such contingencies, but would prefer to know the inter-working between these two - thus pre-payment for data and voice services. Would anyone knowledgeable be interested to exchange thoughts?