Features: 
1) Four billing initialization modes: polar-reverse, 16kHz pulse signal, manually
    and delay automatically charge
2) Pre-payment option, including sum set and payment calculation after a call
3) In-coming-call free or charge
4) Powerful statistic and print function
5) Stores up to 3,000 phone bills, daily records for the latest 100 days
6) Multi-operator mode
7) Transmit tariff rate, clock, initialization and upgrade program rapidly by 
    serial communication tool
8) Rechargeable battery lasts up to 8 hours
9) Each phone line has a remote display for a caller
10) Realizes wireless access by wireless conversion pool