IMPROVED PHONE BOMB 

The above seems overly complicated to me... it would be better to rig the
device as follows: 

  _________            FIRST UNPLUG THE PHONE FROM THE WALL
 /|-------|\  Wire the detonator IN LINE with the wires going to the earpiece,
 ~  |  |   ~  (may need to wire it with a relay so the detonator can receive
  @@@@@@@@    the full line power, not just the audio power to the earpiece)
 @@@@@@@@@@
 @@@@@@@@@@   Pack C4 into the phone body (NOT the handset) and plug it back
             in. When they pick up the phone, power will flow through the
             circuit to the detonator....