Daughter has one of the above phones, on which the speaker has ceased to
work, which I'm guessing is just down to a faulty connection due to the
clam shell design, so in theory should be dead easy to repair.

However, the case is held together by unusual security screws, which has
a tiny 3-way slot which looks something like this from above (if the
ASCII art works):

       |
       |
       |
      / \
     /   \
    /     \

   <- 2mm ->

Any suggestions how to get past these?

Thanks
David