I have a few questions:

(1) If I am the person in the 'locked down geography' how do I call out in the first place?

(2) Are you suggesting I call a friends voicemail or my own? and then it is my friends number that acts as voicemail authentication etc.?

(3) This would involve 'my friend' being able to push the message 'out of his voicemail', to twitter etc. (I think this is what you are saying?)

1. Yes, speak2tweet tacitly assumes that "locked down" area has external PSTN access. But I am visualizing use of this in a "distressed" area as well, like natural calamity, not just political turmoil.
2. Yes, you call your friend's voicemail, but you are not authenticated. I am using a "weak authentication" in the sense only a handful will know your friend's number. The caller is not further authenticated. So theoretically a bad person can flood your friend's VM, but then the friend can delete the offending tweets after the fact.
3. Correct. I am suggesting that my VM provider give me this capability so that I can volunteer it to my friends in need.