Are the contents of text messages logged?

They are stored, of course, on the smartphone or tablet of the sender and the receiver.

But does Verizon (or Cingular or Sprint or whoever) keep and log them? If I sent a text message to a friend 5 years ago asking them to pick up some pizza on his way over, is that message stored and retrievable in 2012?

Would the cell companies tell us either way?