At least in the medical world the security requirements of documents at rest is much higher than ones in transit. So you can't easily do efax because as soon as

At least in the medical world the security requirements of documents at rest is much higher than ones in transit. So you can't easily do efax because as soon as you have a queued pdf its at rest. (It can be done. just not easily.) So when everybody switches over to voip they usually try to keep the old fax machines going which faxing over voip is hit or miss.