<s>
A	O
telephone	B-Protocol
jack	I-Protocol
and	O
a	O
telephone	B-Protocol
plug	I-Protocol
are	O
electrical	B-Protocol
connectors	I-Protocol
for	O
connecting	O
a	O
telephone	O
set	O
or	O
other	O
telecommunications	O
apparatus	O
to	O
the	O
telephone	O
wiring	O
inside	O
a	O
building	O
,	O
establishing	O
a	O
connection	O
to	O
a	O
telephone	O
network	O
.	O
</s>
<s>
The	O
standards	O
for	O
telephone	B-Protocol
jacks	I-Protocol
and	O
plugs	B-Protocol
vary	O
from	O
country	O
to	O
country	O
,	O
though	O
the	O
6P2C	O
style	O
modular	B-Architecture
plug	I-Architecture
has	O
become	O
by	O
far	O
the	O
most	O
common	O
type	O
.	O
</s>
<s>
A	O
connection	O
standard	O
,	O
such	O
as	O
RJ11	O
,	O
specifies	O
not	O
only	O
the	O
physical	O
aspects	O
of	O
an	O
electrical	B-Protocol
connector	I-Protocol
,	O
but	O
also	O
the	O
signal	O
definitions	O
for	O
each	O
contact	O
,	O
and	O
the	O
pinout	B-Application
of	O
the	O
device	O
,	O
i.e.	O
</s>
<s>
Modular	B-Architecture
connectors	I-Architecture
are	O
specified	O
for	O
the	O
registered	B-Protocol
jack	I-Protocol
(	O
RJ	O
)	O
series	O
of	O
connectors	O
,	O
as	O
well	O
as	O
for	O
Ethernet	O
and	O
other	O
connectors	O
,	O
such	O
as	O
4P4C	O
(	O
4	O
position	O
,	O
4	O
contacts	O
)	O
modular	B-Architecture
connectors	I-Architecture
,	O
the	O
de	O
facto	O
standard	O
on	O
handset	O
cords	O
,	O
often	O
improperly	O
referred	O
to	O
as	O
RJ	B-Protocol
connectors	I-Protocol
.	O
</s>
<s>
For	O
this	O
purpose	O
telephone	O
companies	O
developed	O
jacks	O
and	O
plugs	B-Protocol
in	O
various	O
designs	O
with	O
various	O
numbers	O
of	O
contacts	O
.	O
</s>
<s>
The	O
four-prong	O
jack	O
and	O
plug	O
combination	O
was	O
the	O
standard	O
line	O
connection	O
for	O
all	O
portable	O
telephone	O
sets	O
until	O
the	O
conversion	O
to	O
modular	B-Architecture
jacks	I-Architecture
in	O
the	O
1970s	O
,	O
typified	O
by	O
the	O
Registered	B-Protocol
Jack	I-Protocol
standards	O
promulgated	O
in	O
U.S.	O
federal	O
law	O
.	O
</s>
<s>
Many	O
countries	O
initially	O
used	O
different	O
specifications	O
for	O
connectors	O
,	O
and	O
some	O
national	O
connector	O
types	O
remain	O
in	O
service	O
,	O
but	O
few	O
are	O
used	O
for	O
new	O
installations	O
for	O
which	O
modular	B-Architecture
connector	I-Architecture
types	O
are	O
prescribed	O
.	O
</s>
<s>
telephone	O
line	O
to	O
phone	B-Protocol
cord	I-Protocol
:	O
The	O
wall	B-Protocol
jack	I-Protocol
.	O
</s>
<s>
In	O
many	O
residences	O
,	O
though	O
,	O
the	O
boundary	O
between	O
utility-owned	O
and	O
household-owned	O
cabling	O
is	O
a	O
network	O
interface	O
on	O
an	O
outside	O
wall	O
known	O
as	O
the	O
demarcation	O
point	O
;	O
all	O
wall	B-Protocol
jacks	I-Protocol
in	O
the	O
home	O
are	O
part	O
of	O
the	O
household	O
's	O
internal	O
wiring	O
.	O
</s>
<s>
The	O
defining	O
characteristic	O
of	O
wireless	O
telephones	O
is	O
that	O
they	O
do	O
not	O
have	O
a	O
handset	O
cord	O
,	O
and	O
the	O
defining	O
characteristic	O
of	O
mobile	O
telephones	O
is	O
that	O
they	O
do	O
not	O
have	O
a	O
phone	B-Protocol
cord	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
telephone	O
cables	O
in	O
the	O
UK	O
typically	O
have	O
a	O
BS	O
6312	O
(	O
UK	O
standard	O
)	O
plug	O
at	O
the	O
wall	O
end	O
and	O
a	O
6P4C	O
or	O
6P2C	O
modular	B-Architecture
connector	I-Architecture
at	O
the	O
telephone	O
end	O
:	O
this	O
latter	O
may	O
be	O
wired	O
as	O
per	O
the	O
RJ11	O
standard	O
(	O
with	O
pins	O
3	O
and	O
4	O
)	O
,	O
or	O
it	O
may	O
be	O
wired	O
with	O
pins	O
2	O
and	O
5	O
,	O
as	O
a	O
straight-through	O
cable	O
from	O
the	O
BT	O
plug	O
(	O
which	O
uses	O
pins	O
2	O
and	O
5	O
for	O
the	O
line	O
,	O
unlike	O
RJ11	O
,	O
which	O
uses	O
pins	O
3	O
and	O
4	O
)	O
.	O
</s>
<s>
Thus	O
cables	O
are	O
not	O
in	O
general	O
compatible	O
between	O
different	O
phones	O
,	O
as	O
the	O
phone	O
base	O
may	O
have	O
a	O
socket	O
with	O
pins	O
2	O
and	O
5	O
(	O
requiring	O
a	O
straight-through	O
cable	O
)	O
,	O
or	O
have	O
an	O
RJ11	O
socket	O
(	O
requiring	O
a	O
crossover	B-Protocol
cable	I-Protocol
)	O
.	O
</s>
<s>
When	O
modular	B-Architecture
connectors	I-Architecture
are	O
used	O
,	O
the	O
latch	O
release	O
of	O
the	O
connector	O
should	O
be	O
on	O
the	O
ridge	O
side	O
of	O
flat	O
phone	O
wire	O
in	O
order	O
to	O
maintain	O
polarity	O
.	O
</s>
<s>
50-pin	O
miniature	B-Protocol
ribbon	I-Protocol
connector	I-Protocol
for	O
RJ21X	O
,	O
used	O
for	O
up	O
to	O
25	O
lines	O
for	O
multiline	O
phones	O
such	O
as	O
the	O
ITT	O
2564	O
,	O
key	O
telephone	O
systems	O
such	O
as	O
the	O
1A2	O
Key	O
System	O
,	O
and	O
PBX	B-Device
systems	O
.	O
</s>
<s>
This	O
list	O
covers	O
only	O
single-line	O
telephone	B-Protocol
plugs	I-Protocol
commonly	O
used	O
in	O
homes	O
and	O
other	O
small	O
installations	O
;	O
there	O
are	O
44	O
different	O
variations	O
of	O
plugs	B-Protocol
,	O
including	O
an	O
Israeli	O
version	O
of	O
BS6312	O
with	O
different	O
internal	O
wiring	O
of	O
the	O
pins	O
,	O
plus	O
hard	O
wiring	O
to	O
a	O
junction	O
box	O
with	O
no	O
adapter	O
.	O
</s>
<s>
Special	O
telephone	O
sets	O
use	O
a	O
variety	O
of	O
special	O
plugs	B-Protocol
,	O
for	O
example	O
micro	B-Protocol
ribbon	I-Protocol
for	O
key	O
telephone	O
systems	O
.	O
</s>
