56K dialup is sufficient, though I'd expect a slight increase in stales from the increased latency.
56K would not be too slow, as its faster than no connection (and sufficient) in the event of a failure.
Failure of both connections is a non-issue. If we are talking about a failure of both phone lines and DSL/cables lines at the same time, sounds like a serious event such as a storm. In which case the power will be out anyway. So its moot.
I love ignorance.
No, we do not.
We talk of someone pulling down the phone cable. Can happen outside of a storm just by accident. if you are in the US, those lines are likely over land - have a car crash into it and they both go down. Have some builder cut the cable and they both go down. have a fire in the phone company and they both go down.
Been there, seen that.
There is no reason not to run the backup over something that runs over separate lines. 3g for example.
I give you one example of my "CoinCore" data center we are signing contracts for monday
In this case it is an old factory - I get DSL there installed as mains, and on top I have the nice power coming in by high voltage lines (power station over the street in the complex - not even 30 meters, taking it down to our 408 volt 3 phease, i.e. 230 volt).
There are many scenarios I can envision where DSL or power can fail separately. There is nothing I can do for pwoer (USV are just not worth it), but I can:
* Run a local pool proxy, so there is not a ton of open connections for long poll out of the building.
* Run my backup over 3g / UMTS or even LTE when it comes (IF it comes).
In cae some stupid renovation somewhere (not unlikely at the moment) cuts the phone line.... nothing happens
The price is neglegible (actually it is - I get it into a package with the DSL line).