I think if I found the solution: temporary, but may be solution (I'm still testing/trying).
I think the problem resides in the notification of intinerancia which is enabled by default. in a day makes it I have seen that when the screen is lit and changing band, eg from 3g to h +, crashes ... Conversely also happens: if screen turns off and the screen is locked ... I have removed the option and I left that "never notify roaming" and it seems the w300 is stable.
Try us and you comment ...