It works perfectly with one of my older Fido phones, even without a SIM card.
If you ever decide to try it yourself, please remember : don't hang up and tell the operator you were testing if your older phone could dial 911 without being activated.
This is required by the law if i'm not mistaken, in both the USA and Canada. So yes, keep an old phone in your glovebox with a cigarette lighter adapter.
Hope this helps!
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"The only easy day was yesterday."