Is it permissible to utilize the full value of the mobile phone credit balance, knowing that it exceeds the business's needs, or must one limit it only to what serves the business?

If the system dictates that the value of calls granted to the employee is an allowance for communications, such that he covers any deficit from his own pocket, then he is permitted to use the remaining balance for his personal affairs. However, if the state grants him the value for use in its specific matters, and increases it if it is insufficient, then it is not permissible to use any part of it for purposes other than the specified one, except with the permission of the authorized person.