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.
Soluble grit is digested by the hen and contains calcium, most of which is used to form strong egg shells. The majority of an egg-shell is made up of calcium carbonate and a constant supply of oyster shell grit ensures they have sufficient calcium in their bodies.