For Smart, it’s because, contrary to their name, they’re not doing the smart thing. They LIMIT the number of messages their subscribers can send even when enrolled in their unlitxt promo. We can only send at an average of 420 messages a day. You can read about how smart they are here, here, here and here.
So what’s the smart thing to do? Until they become truthful to their subscribers, Switch to Globe! :p
So now we know, we will no longer get frustrated.