SIP Express Router: Free GPL-ed SIP server (registrar, proxy, redirect)
http://iptel.org/ser/features
De-facto standard
SER: domains, subscribers
Routing language
extension modules
http://iptel.org/download

INVITE: initiates sessions
ACK
CANCEL
BYE
REGISTER
OPTIONS
SIP extension methods:
SUBSCRIBE/NOTIFY/MESSAGE: instant messaging
REFER: call transfer
PRACK: provisional reliable responses
INFO
UPDATE

SIP Phones (User-Agents)
SIP Servers (Registratar, Proxy, Redirect)
SIP PSTN Gateways
Application Servers (Media Servers)

We have customers using Vonage.
With Voicent software, you can set call interval so the dialer will not
continuously using the phone line. This seems to satify some phone
company’s unlimited calling plan.
> I am doing the research and set up for a friend in the home loan business. We
> are intent on trying your dialer software and […]