Hi hostedtelephone,
Gee, I thought I was dealing with a connectivity professional. Silly me, I completely forgot to look at your job designation. Programmer. That says it all really as your responses are exactly what I here from those same disconnected IT pros. I'd say you're at least a couple layers of abstraction away from reality. The other folks with the same job title have a far more accurate feel for what makes a workers telephone go ring, ring. And they make sure that phone usually does ring when it should.
What happens when a line gets noisy to your clients? Well, DSL usually cuts out, so does cable, but there is no analog equivalent with which to hear problems. Normally you will deliver your service on the least expensive transport, which excludes something reliable like a T1 in any flavour. That means the connection dies in silence as far as the telco or cable provider is concerned. Perfect for anything beyond a small office (use your cell phones) or retail store. Anything else, like a factory depends on 911 response as a legal responsibility. I guess it's okay, because today cell phones have GPS built in.
For the poor fella using a KEY system on POTS lines, they call the telco in between other calls and report the noise. Or, they use another line. Either way, those people are still in business.
As for "tin on the wall", or in a rack (cause we put systems in that way as well), it's true that the Magix is one of the most reliable systems out there. The Partner is pretty reliable as long as you use the newer 5 slot carrier, hate those two slot demons though! But, the Magix is a bear to get fancy with for most people. You have to continually "fake it out" to get what you want. I'll even push for Toshiba and Panasonic systems. What I can't agree with is almost anything Nortel designed. They are junk, expensive junk as soon as you try to do anything with them. You can cover a wall with that crap and still be out performed by a small Partner or Magix system, with a savings in power to boot. I'm not kidding, they are not reliable systems, sorry. Even the great BCM has a propensity to fail, and that is very probably what really killed Nortel. Not the CO switches they sold to companies that went belly up. I highly doubt that story.
Bottom line. Hosted solutions are not reliable, period. We use these, but the hosting hardware is hung on the client's premises and runs a pile of SIP phones around the world. Yep, we have done those as well. Within the building, you can't beat digital phones, and you do not lose any features doing it that way. You still have screen pops and all the other toys, so a hosted (vapour ware) solution gains you nothing, unless you like to go home 'cause you can't work.
-Chris