Wire cutting/stripping abilities
A telephone handset (non wireless) with buttons
2 needles (used for hand sewing)
RJ-11 jack/plug with wire attached
Plug to wire type thing (I got mine from a computer cases hdd led)
The beige box can be used to hijack a telephone landline, if you remove the mic it can be a wire tap.
If your really want to put some effort in, you could add a wireless module for long term surveliance, although, if you do, you are obviously some sort of freak. (pun intended)
Sorry about the pics (webcam)
Step 1: Snip 'n' Strip
NOTE: the jack used from the base to the handset is not usually an RJ-11, check and if it is give the jack some wire because you might use it later, but if it isn't, then cut as close to the jack as possible.