I have a similar problem with BT BB/speedtouch modem, but perhaps differs in that modem will no rconnect when recovering PC from Standby mode. I have to reboot each time. BT say that USB is at fault for not kicking from standby but I query this. On the other hand I may need to download new drivers for USB (from where i don't know!).
I know that this does not solve your problem but i will post any further info I have.