Has anyone successfully implemented Internet based faxing both inbound and outbound?

I would be curious to learn what products you used and what pitfalls you ran into. I am looking for a solution that does not use a phone line and uses strictly TCP/IP.

Any discussion would be appreciated

It's fairly easy, you should start by reading some docs about G.729 as that's the most widely used protocol for IP based fax.

However be advised that when using TCP/IP for faxes you need to set the compression level to the minimum and therefore it uses a nice amount of bandwidth, so you'll need at least about 128kbps free (continuous) and have a close to zero latency between the sender and the receiver (faxes don't wait as humans do when it's just voice), maybe something under 20ms.

is there an application already developed?

In the unlikely event that you're planning a service to be used (or could be used) to send unsolicited fax spam to people, note that California has passed legislation which makes this illegal and comes with a $1,500 per incident fine.

If you are hosting a service that provides this and one of your users takes advantage of this to send fax spam, you are also liable for breaking the law. I'm just making sure that you know this before you take on this project.

FYI

The purpose to know about this is for commercial purposes only. I want to offer a free fax to email program that for a fee my customer will be able to fax his document to an email address and posibly to send it to a relay that will get the emal and forward it to a real fax machine.

Just like efax. but I don't have their budget so, I'm looking for a free utility that I could start learning this technology and then see what happens...

I'm looking for such software as well. It should be a script installed at remote web server, so I could code a web page to interact with it.

Erm.. www.hotscripts.com i saw a web that we can use Via FAX send thru computer attechment, and etc.. there is a gateway for that..