I dont know your phone systems/networks but is verizon a GSM network?
If so you can manually roam by going throught the roaming menu options in the phone.
Also GSM networks have an emergency number built into the phone and networks which is 112
This number will contact the emergency number through the strongest signal cell available. The phone doesn't even have to be connected to any network, it just needs power.

You can also have a selection of GSM prepaid SIM cards handy to slip into the phone to connect through which ever network is available in an emergency, but use the cheapest SIM card for day to day use.

I am not sure what systems are available to you but that is some info on the GSM system available in Australia, Europe & the US (at least in some areas of the US)