This is a fantastic idea, although they'd need to have several carriers to make it feasible (what if someone uses t-mobile instead of verizon?
Does a similar thing happen in the US?
Also seems like a perfect application for those Stingrays the police have stockpiled.
http://s9.postimg.org/umb1a3tjz/s5570.jpg
Besides 911 there are probably a few other emergency numbers in the US which are open on all cellphones, as well as the emergency broadcast system which will display push notifications on every modern cellphone in such cases as natural disasters.
LTE, however, is making this less of an issue and in theory an LTE capable phone should be able to make an emergency call from any network.
Government surveillance already has multi-band and protocol mobile tower stand-ins.