A PIN message is not the same as a BBM message. Unless that person has you on ignore, then you can send as many PIN messages to them as you like. If I receive a BBM request from someone I do not recognize, then I usually fire them a quick PIN asking them who they are, and how they got my PIN.
You will not be able to send a BBM message to a contact unless they are on your list, and they have to accept your request. Just like other people have to accept yours if you want to message each other.
