<s>
Centrex	B-Device
is	O
a	O
portmanteau	O
of	O
central	O
exchange	O
,	O
a	O
kind	O
of	O
telephone	O
exchange	O
.	O
</s>
<s>
It	O
provides	O
functions	O
similar	O
to	O
a	O
PBX	B-Device
,	O
but	O
is	O
provisioned	O
with	O
equipment	O
owned	O
by	O
,	O
and	O
located	O
at	O
,	O
the	O
telephone	O
company	O
premises	O
.	O
</s>
<s>
Centrex	B-Device
service	I-Device
was	O
first	O
installed	O
in	O
the	O
early	O
1960s	O
in	O
New	O
York	O
's	O
financial	O
district	O
by	O
New	O
York	O
Telephone	O
.	O
</s>
<s>
As	O
of	O
2003	O
,	O
it	O
was	O
estimated	O
that	O
there	O
were	O
20	O
million	O
Centrex	B-Device
lines	O
installed	O
worldwide	O
by	O
20	O
telephone	O
companies	O
,	O
with	O
the	O
most	O
installations	O
in	O
the	O
United	O
States	O
(	O
15	O
million	O
)	O
,	O
Canada	O
(	O
2	O
million	O
)	O
,	O
and	O
the	O
United	O
Kingdom	O
(	O
1	O
million	O
)	O
.	O
</s>
<s>
In	O
terms	O
of	O
user-visible	O
features	O
,	O
Centrex	B-Device
and	O
PBX	B-Device
are	O
similar	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
the	O
usage	O
of	O
Centrex	B-Device
lines	O
has	O
fallen	O
from	O
16.5	O
million	O
in	O
2002	O
to	O
10.7	O
million	O
in	O
2008	O
as	O
users	O
transition	O
to	O
IP-PBX	O
(	O
through	O
VoIP	O
)	O
.	O
</s>
<s>
Centrex	B-Device
continues	O
to	O
be	O
used	O
by	O
large	O
institutions	O
,	O
government	O
agencies	O
,	O
and	O
universities	O
as	O
most	O
of	O
the	O
equipment	O
has	O
already	O
been	O
paid	O
for	O
,	O
though	O
leasing	O
Centrex	B-Device
lines	O
may	O
be	O
more	O
expensive	O
.	O
</s>
