Actually I want to know whether keypad phones are allowed to carry in flights and how many phones are allowed in a flight. Which bag are they allowed in: cabin bag or check-in luggage?
There are two factors:
radio transmit/emission (e.g. to (try to) connect to mobile network). This doesn't depend on the type of phone (but if it transmit on non standard frequencies), but on the airplane. You should check your airline website, to see if your plane has micro cell for phones (usually it is advertised). Note: you cannot use them below height (from ground) 3000m (10000 feet)
batteries: Rechargeable batteries could be an hazard, so it is better to have in hand baggage (not in checked baggage). Some batteries are forbidden in checked baggage, so better to be in the safer side, if you are not an expert on batteries type and battery capacity.