<s>
A	O
telephone	B-Protocol
VoIP	I-Protocol
adapter	I-Protocol
(	O
TVA	O
)	O
,	O
also	O
called	O
digital	B-Protocol
telephone	I-Protocol
adapter	I-Protocol
,	O
is	O
a	O
device	O
that	O
allows	O
digital	O
PBX	O
(	O
Private	B-Device
branch	I-Device
exchange	I-Device
)	O
telephone	O
handsets	O
to	O
be	O
connected	O
to	O
a	O
VoIP	O
network	O
,	O
using	O
,	O
for	O
example	O
,	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
.	O
</s>
<s>
An	O
ATA	O
(	O
analog	B-Protocol
telephone	I-Protocol
adapter	I-Protocol
)	O
allows	O
analog	O
phones	O
to	O
be	O
connected	O
to	O
VoIP	O
networks	O
.	O
</s>
<s>
A	O
Centrex	B-Device
TVA	O
VoIP	O
enables	O
centrex	B-Device
phones	O
and	O
analog-based	O
Centrex	B-Device
phones	O
like	O
BT	O
Featureline	O
.	O
</s>
