String literal. A string literal or anonymous string is a type of literal in programming for the representation of a string value within the source code of a computer program.
As usual, the devil is in the details. For instance, with some prepaid wireless plans, your minutes are only good for a limited time, usually 30 to 90 days. If you don't use them before they expire, they are simply subtracted from your account anyway.
That does sound odd! It will depend on what prepaid plan you're using as to how long the credit will last. For example the old $2 a day 4G ready prepaid plan, if only $10 is applied the credit will expire after 10 days that being said the service shouldn't expire at this point in time.