There is no requirement that an API be provided to law enforcement. That "sendmessage" method could come down to someone on the law enforcement side getting on the phone with Apple or Google or Microsoft or a service provider and telling them the numbers to kill.
This is assuming that Apple or Google or whoever even can flip the kill switch without the assistance of the phone's authorized user. They could easily design the kill switch system so that the person flipping the switch has to know the authorized user's password [1]. There is nothing in the bill that I see that says they have to design the kill mechanism to allow law enforcement or the manufacturer or the carrier to be able to use it.
[1] For instance, the phone could ask for your iCloud or Google account information when you set up the kill switch for the first time, and then it could store on the phone a hash of the concatenation of your password and the phone serial number. The kill switch mechanism could require that the kill command include that hash, thus proving to the phone that the sender had access to your password.
You don't know what you are talking about.
EDIT: yes, please, go ahead and explain how you're going to get phone's location geographically. Hint: not everybody has data turned on always. Or GPS.
This is not a Batman movie you know
Its not perfect, but they can get your position by just measuring your signal strength to the multiple towers and triangulate the rest.
No, this is not a batman movie. For more, check out http://worldwide.espacenet.com/publicationDetails/biblio?CC=...
Phone[] phones = GetPhonesByGeo(radius=50, lat=102.23412323, lon=-129.4342424);
foreach(Phone p in phones) { p.sendmessage("Lock"); }
func GetPhonesByGeo(){ // your tax dollars at work }