Can i get a blackberry with watts app n not pay for the actual bbm service?

i want to buy an actual black berry phone and just download the watts app but not have to pay monthly for the actual bbm service... will watts app work even if i dnt hav the bb servise but just the phone??? n i wanted to no wat is a gd phone company? would it be AT and T or somthin else?? just to make phonecalls n text measages to people who who dnt hav a blackberry... pls help bcz i really need to no this info before i buy a new phone n if bbm doesnt work out for me what is a goood phone thats for a 15-16 year old girl (any color) n wat r the prices i need a cool phone too thnx! :)