With pay as you go or other account setup if the billing is overdue then calls cannot be made in or out. At least people should be able to call the number to ensure contact in emergencies. Some countries operate that way and it is very helpful. This was a problem when my son was pay as you go and would forget to top up.
You can top up through the My Telus web interface. You can set up automatic top ups. You can buy a voucher at a retail location and call 611.
Canada charges for calls in both directions. Allowing incoming calls without an account would be problematic, as there is no way to determine when the account becomes inactive.
Those countries that "operate that way" charge the calling party for the airtime. So people can have prepaid phones and not pay airtime for when they are called.
That's why you see different long distance charges to many countries when it is a landline versus a mobile.
I'd certainly much rather have it the way it is here than to pay someone else's airtime when I call their mobile. I believe that the phone should still be able to call 911 for that type of emergency.
I had a number in Indonesia. I was only charged a local rate if I called a friend who had an Indonesian number but was out of country. I could receive text messages out of country at no charge. This was a monthly billed account.
For pre paid cards in Indonesia if you ran out of credit you could still receive calls but not make calls. This worked well because you would not call 911 if your kids forgot to top up but you could call to find out where they are.
Charges for calls and text messages much much cheaper.
Just too bad I can't set a roaming limit on my son's number.
We have a system here too, which works pretty well for most people. Pay your bill on postpaid and make sure you have top up credit on prepaid. Having the phone not work when it isn't topped up is a built-in education system to train people to top up. as an accommodation, the phone will call 911 when it is out of load, but not other "emergencies" Your request to "have it work" when it runs out means that people could use phones without paying for them, or have other people pay their airtime (like in some other countries).
It is true that mobile phones are cheaper in countries like Indonesia, but I prefer to live somewhere that I can drink the tap water and drive to where I'm going without some of the worst traffic jams in the world (Jakarta for example).
We have a similar system for cars. When they run out of gas (or charge on an electric one) they stop working. It is imperative to remember to top them up at a filling station before running out, or you can end up stuck in the middle of nowhere.
The solution to this problem lies with getting your son to learn how phones work here and to make sure to "remember" to top it up.