The People's Operator has a US based customer service team. They are positioned as a carrier who is socially conscious and they will donate 10% of your monthly bill to a charity of your choice. You don't need to do anything, TPO will take care of it all for you.
Seashells contain calcium carbonate. The calcium carbonate reacts with the acid in the vinegar and causes carbon dioxide bubbles to form. Even though the acid in vinegar is weak it can, over a period of time, dissolve shells.
The most common calcium supplements are made of carbonate, citrate (which is easier to digest than carbonate), dolomite, di-calcium phosphate, tri-calcium phosphate, coral, oyster shell or bone meal, and all variations of amino-acid chelated calcium (which are the most bioavailable of all the above forms of calcium).