I have an iphone 5S my friend has a Blackberry 9320 - she has upgraded with the latest software available for her handset and I have installed the BBM app - we are able to chat via the BBM app but not make calls at all - whenever I try calling from my iphone it says she's unavailable, yet I can call someone who has the BBM app on their iphone, is there a problem calling from iphone to blackberry?