First of all, let me affirm that I am not particularly tech minded.
I pay an annual subscription of THB2,500 to AIS for data. I use the data so that I can make/receive calls via Line/skype/WhatsApp etc. when out and about. I AM aware of the use of hotspots in bars/cafes etc. but prefer not to rely on them. I also use my phone as a hotspot at home which enables me to operate my laptop for banking/browsing etc. This works fine.
When I renewed with AIS earlier this year, I asked them to put THB50 on my phone for normal phone calls. As far as I am aware, that THB50 still exists as I hardly ever make "normal" phone calls, but I felt that it was good insurance in case I needed it.
A friend has a mobile Wi-Fi (MiFi) device and has suggested that I should buy one --- for just a few hundred baht with no subscriptions payable. I am a little sceptical about doing this, hence the reason for the question in the title of this thread. My friend said that "some" data is still available on his phone even when he leaves home without the Mi-Fi device, but I can't see how this is possible.
Coming back to the question in the thread title:
Would the answer be this? If I don't renew my AIS subscription, saving THB2,500pa, but instead, buy a MiFi device to use my laptop at home, I can still access the internet when out and about provided that I TAKE MY MOBILE MiFi DEVICE WITH ME.