Fast and cheapest, get 3 feet of 23AWG CAT6 and pull out a pair, strip about 2" off of one end and enough on the other end to wrap around your test leads. Go off hook on your set and lightly push the stripped conductors down ever so slightly to pull dialtone (over an existing jumper).
If you have C4's or C5's without jumpers 24AWG will work fine, but if you have an existing jumper that's 24AWG then use a 23AWG test wire because the pins are already spread and this one will make better contact.
