I once tried this on globe and called the cs hotline. Upon converging on the tech guys of globe they found out that that my sims data allocation versus the generated airtime balance wasn't reasonable (since I've been using the sim on vpns) and they also found out that I'm using the vpn service and told me that it's beyond the law of ntc...blah...blah...blah. So to cut the story short, there is a chance that they will trace you upon your query and make law suits claiming to be using ïllêgâl connection.
Advice: If you're not experiencing this kind of treatment, congratulations. But, prepaid sims are lot more cheaper than a bail for something that's unreasonable.