Voice telephone calls, faxing over VoIP still has a lot of room to improve.
Have you ever tried to fax on your residential VoIP line? I have, and it didn't go well. After doing some research on the subject I found out that the voice traffic and the Fax traffic are best run over two different codecs. This is why when most VoIP carriers sell you a business account they include a free additional fax line with the faxing specific codec to allow for faxing.
Faxing on a Voice VoIP line is possible but not recommended. You can fax a page or two over your Voice VoIP line but it may take you several attempts to accomplish. The reason is when the fax tone is digitized into packets, there is packet loss. Packet loss on a voice is not that critical because even with a little packet loss, you can still hear and understand what the person is saying. But, when there is packet loss on a fax, any little bit can really mess up the fax. The result can be a bad fax, error message, or even a dropped call. When faxing over a Fax Codec, the loss of packets is minimized and faxes generally make it to its destination, but in the case of a large fax (10+ pages) your chances of a successful fax diminish. It is recommended that a customer who is planning on faxing quite a bit get a fax machine that also doubles as a scanner and can convert potential faxes into a .PDF file so if the fax over VoIP does not work, the customer can email the fax.
Programmers are coming up with a better codec all the time, so it is only a matter of time before VoIP providers come up with a more reliable faxing VoIP codec. VoIP is here to stay and the VoIP providers are trying to overcome all of the objections from small businesses to gain their business, and faxing is a large issue for small businesses. I have the utmost confidence in VoIP providers to come up with a solution that is viable by the end of 2005 or earlier.
Faxing is only one of the things to consider before choosing a VoIP solution. In fact, there are many things to consider when choosing a VoIP provider.