There are no sign up fees, billing fees, participation fees or extra fees of any kind, other than the charges for actual usage and a 3% Federal Excise Tax levied by the FCC for all long distance traffic going through the USA.  Your customer may sign up and try the service without risk or obligation.

     To minimize fraud, the customer is not, by default, allowed to change his callback number. For those customer wishing to change their callback numbers remotely, an option on the order form is provided.

    An Extension Feature, sometimes referred to as Auto-Route is available using either Voice Prompts or DTMF Tones.  The Voice Extension Feature is used when the callback is directed to a live receptionist.  The system repeats: Please connect this call to extension ###. If DTMF Tones are selected, the tones representing the desired extension are generated when the callback is answered.

    Regarding Mobil/Cellular phones, callback systems are unaware of what is on the other end of the line when a return callback is placed.  In general, this means that if a Mobil phone receives the call, it will work just as if the call came from any other party.  The uses is billed for his usage just as though the call was made from a stationary phone.   If the Cellular provider charges for incoming calls, then those charges will be billed by the Cellular provider.