If you are on OS 4.2 then adding them to your address book along with the pin number helped me alot. Then I would add them as a contact from BBM and select them from the address book list instead of using use once. Worked every time for me then. Give the links a shot if you are on 4.5 and having issues.
Once you make sure you have a data plan, double check and make sure you have their PIN/e-mail address entered correctly in their contact information. If it isn't exact, it will always just say pending.