Messages fail to deliver to one particular PIN

A friend of mine has service with Vodafone AU and is over in the US right now. She receives my PIN messages a BBM requests but any messages she sends me (even replies) fail. She's able to send and receive messages with everyone else's Blackberry, as can I. She usually roams on AT&T while in the US and I switched her over T-Mobile but it had no effect. I'm on T-Mobile, but I don't see it being a problem with my network as she can send and receive messages to and from other T-Mobile USA BB users. Any idea why she can't send a message to my PIN and my PIN alone?

Posted from my CrackBerry at wapforums.crackberry.com

Update:

When we moved out of the area, PIN messages that had been sent to me days earlier were finally delivered. Any ideas on how or why this happened?

Probably one of those strange network phenomenons. I often have issues with TMO BBs and Sprint BBs but not with BBM but texting, it's a pain.