I'm a BB user, why can't I send message to iPhone and Android users in BBM?

BlackBerry Messenger is now available for Android and iPhone. I added friends who are Android and iPhone users. But I can't send messages to them. Other BB users can send messages to them. I'm in postpaid, but a postpaid friend can send to them. I tried deleting them and adding them again, I also tried removing my battery and memory card, all to no avail. What else do I do? Uninstall my BBM?

I'd recommend calling tech support