For this Instructable you will need:
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
pretty self explanatory.
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.
Step 2: Ze Needles
Very simple, just attatch the wires to ze needles and you'r good.
if you arent out of solder, it is highly recomended, but if you are, just give it the good ol' twist and tape.
10 bonus points to anyone who can thread the wire through the eye of the needle
Step 3: Optional: RJ-11 Jack
the benefits of having the RJ is that you can use it at any public port and not look anywhere near as suspicious as injecting neddles into wires :P
All you have do to is get the RJ-11 and something which you can attatch to both the needles and the RJ, for this i used the leads from and old computers HDD LED.
Step 4: Using
If you made the adapter in the previous step, you can use it as a normal phone, but where's the fun in that. using is pretty straightforward: Find phoneline, inject green needle into green wire, inject red needle into red wire, YAY! you're an amateur phreak!
you can find phonelines in a box on every house, but (in aus at least) they are secured with a 5point star hole in middle screw, you can find hubs that look sorta like missiles, but they are secured with a key, or you can go into the city, find the telstra(or AT&T whatever) building, but it is secured with a receptionist(idk).
if you have to, you can get into at least the 1st two fairly easily, but it is illegal, so don't.
also it might take you a while to get used to the needles, so be careful or there will be blood.