A couple discount stores (ALDI, Tchibo) are already offering low priced rates in Germany since last year. Now Wal-mart is also getting into this game. The pricing and what carriers Wal-mart will offer is not revealed yet.
Mobile phone rates have come down in Germany recently through Internet only providers like Simyo and the offers of discount stores. The rates were to high long enough actually. So this is a great development. And it is still just the beginning.
More details on Teltarif (German), via Heise (German). See also the Mango Mobile site (German).