Also called butt-in sets. I don't do a lot of
telco work, but it's a lifesaver if your working in a
phoneless
server room and need to
dial out or
call someone. With a bit of phone
savvy, you can probably find a line you can "
borrow".
These are basically
ruggedized DTMF phones typically used on
POTS lines with tough leads that go to a
alligator clips instead of a
RJ-11 plug. The clips are designed to clamp onto wires with or without the rubber
insulation (they use little
pins for piercing insulation w/o really damaging the wire). They can also
jack right into a 110-style block (the thing that
converts telco
wiring into something you can plug into your
phone system). If you have a
tone and probe set, you can plug the
inductive amplifier into the phone for either
quiet probing or so you can hear quiet
tones in a
loud room. With two sets and a nine
volt battery, you can
talk with another set across some distance of
wire, like a
field telephone. Very useful.
Most butt sets have a
monitor/talk switch. In talk the phone acts like a normal phone that is
off hook, you can
speak, listen and
dial. Switching to monitor will hang up, no dialing or talking but the phone will
ring in this mode
and you can still hear.
Hence, if
someone is on the
line and your are in monitor, you can hear both parties on the line but they won't know the wiser: ala the name "butt-in set". Of course this is
illegal, and you could be given away if you
fumble the wires, make a
crappy tap or they have some
detection hardware.
Another common feature is a
polarity light which helps you make sure the two wires of a phone line ("
ring" and "
tip") are the right way around. However the set (and most phones, I think) will work no matter which way the wires are headed.
I've only owned two
types of butt set:
great and
crap.
A great set is the
Harris TS22A. It runs off a nine volt battery, has a tough,
metal belt hook and
awesome orange finish. The 22A has features like two-way
speakerphone,
speed dial and other stuff I can't even
remember. It is a real battery
miser, I've only changed it once for the sake of
neglect. You can drop this phone through a
ceiling tile, watch it bounce down every
rung of your
ladder and crash onto the floor, then merely
dust it off and get back to work. After fixing the tile, oops.
This unit cost about $325 when I got it, probably $290 or so now. I only paid $100 tho, as a
telco friend stole it from
work and sold it to me
brand new in the box.
A
crappy set is the Model 390, by
Progressive Electronics. It is powered by a
proprietary battery (the phone must be sent back to Progressive for battery swapping), has a not-bad cord, plastic belt hook and is generally not built as well. I bought my first one for only $80 (they're really $160, the
vendor owed me a favor) and within a few months it wouldn't dial. It just stopped making tones. The vendor said the battery should still be good, and that he has lots of these phones with that problem. (
great....) He swapped it for a new one and within another few months it stopped with the same problem. I haven't performed an
autopsy to find out if the battery is at
fault, but
I don't really care. I just use my Harris.
There are special
breeds of these phones that can talk on and troubleshoot specific
PBX systems,
ADSL lines, and (I'd imagine)
ISDN. I've only gotten to see these pricey
monsters once or twice though, no real experience.