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Small piece of expectations management here: paying more for a service isn't going to make it more reliable.

Second piece of expectations management, no single piece of technology or service can ever be relied to never fail. If it's safety critical, you should get a backup, preferably from a different company.

In the end telephone is a 'secondary' service for VM. It's not particularly unique or competitive, if you are having trouble with it the easiest solution is to switch to a different provider.