it is cheaper and call quality is often as good!
VOIP (Voice Over Internet Protocol) allows a voice
conversation to be carried over the same line or connection used
for accessing the internet.
Because the transfer of data over the internet is carried out in
vast quantities at huge speeds, the "bits" (packets) making
up the voice conversations can be carried easily, and since the
cost of most internet connections are based upon bandwidth considerations,
VOIP is carried for very little additional cost - if any. So to
call someone else on the same service as you have is like dialling
an extension number in an office, and often costs nothing.
If your call is going to a telephone number on another network or
in another country, the VOIP can be carried most of the distance
to an internet centre nearest the physical location of the person
you are calling, and then conventional telephony (cable or wireless)
is used to deliver the call on the final leg of its journey. The
return journey is made in reverse to give you a two way telephone
conversation. Because so much of the physical distance covered by
the VOIP packets is via the internet (using Internet Protcol), call
prices are lower than conventional telephony.