Sure it's just an MVNO (mobile virtual network operator), which means that Wal-Mart is essentially reselling T-Mobile's service, but this is still major news:

Wal-Mart Stores Inc. said Monday that it is introducing the first cell phone plan that uses the chain's own branding, further demonstrating its clout in getting special deals from wireless carriers.

The Wal-Mart Family Mobile service will run on T-Mobile USA's network. Unlimited calling and texting will cost $45 per month for the first line and $25 for each additional line for the family. The service will be offered starting next week in most of its stores across the nation.

Read the entire press release here.