SpareOne Emergency Phone
spareone.com
spareone.com
Also, at least in the UK and I believe europe, if you put any SIM into a phone, nomatter if it has a contract or not. You will be able to call 911/999/emergency services. So you can get a SIM for a each network and have them spare to cover all permutations.
Though as I said, nice idea, just expensive for what it is. Realy needs to be sub $30.