In the US, “postpaid” mobile phone bills where you use your phone and then get charged for your usage are the most common, but if you’re worried about surprise bills, you can do prepaid billing instead, in which case instead of being extended potentially-surprising amount of credit, the expensive thing you’re trying to do just doesn’t work. They also usually make it easy to add more money to your account in case you really do want to do something like expensive international roaming.
In the US, “postpaid” mobile phone bills where you use your phone and then get charged for your usage are the most common, but if you’re worried about surprise bills, you can do prepaid billing instead, in which case instead of being extended potentially-surprising amount of credit, the expensive thing you’re trying to do just doesn’t work. They also usually make it easy to add more money to your account in case you really do want to do something like expensive international roaming.