Ability to send messages without calling

[martinbomio]

@stephenlb I am not sure if this is needed but it is useful for my use case so I opened this PR. Feel free to not merge it if you think it is not necessary.

Basically, adds the ability to send a message to another phone using the pubnub channel. (without needing to start the call first).

var phone = PHONE({...})
phone.ready(function() {
    phone.send("Hi!", someOtherPhoneNumber);
})

[stephenlb]

makes sense to me!