Description:

SIPFwd is a SIP forwarding daemon that acts as a stateless SIP proxy to
essentially forward a SIP address to another SIP server. This is useful
if you already have an account with a SIP provider, but aren't too happy
about the SIP URL you got and instead prefer to use a SIP URL with your
own domain name (but don't want to run a full-blown SIP server like
Asterisk or OpenSER).

So it allows you to use and publish SIP URLs of the form
sip:user@example.com with the minimum possible effort.

Of course, your existing SIP provider has to allow incoming connections
via SIP (unfortunately, some providers choose to block direct SIP connections
and only allow connections via PSTN).