I opened 2 accounts with same name one for the 800k and one for daily spending no problem with K bank.
But be prepared to get all docs with you.
Passport, visa info, proof of residence (lease contract - make sure all name/passport # match on lease contract some bank examine them letter by letter). Get to bank early it took them quite sometimes to finish 1 account.
Just use your download voice app to make calls and text free.
If need to call internationally, than need to deposit some small amount in yr google wallet ie $10.00. international call charges varies from 0.05 cents per min or higher.
There is a chart in ggv which you can check each country / min for voice call.
oh yes, and you are exactly right. I am under the impression that NON OA cannot be extended within Thailand. And only NON O can be issued within Thailand. It is good to know that it can be and you have done it multiple times. Thanks.