These are temporary us phone numbers or also called us numbers. This means that they are only available for a short period of time. Some us phone numbers last for several months, others only a few days.
Please do not use such a USA number for important text messages such as passwords, private text messages to friends or for phone verification on websites. Anyone could take over your account by reading the text messages of these us phone numbers.
If you do not live in the United States and still want to use a particular site or web that only accepts us users, it is necessary to have a USA phone number / american phone number to verify your account.
Most websites that require phone number verification have a limit on how often you can use a phone number. In this case it can happen that some of our us phone numbers are blocked. But this is not a big problem. Just use one of our other us phone numbers.