Extra lines will cost $25 each (the Verizon/Wal-Mart plan doesn't offer any discount for additional lines). Wal-Mart Family Mobile plans won't require contract agreements even though they're postpaid rather than prepaid. You'll have to pay a little bit more for data, though.
Don't be too shocked and amazed at this announcement; the retailer isn't erecting cell phone towers or building a global communications network. Rather, your Wal-Mart Family Mobile phone will technically be running on T-Mobile's network, but it will be locked to Wal-Mart's plan and customer support.
The most surprising aspect of the news is actually that the plan is cheaper than comparable plans on T-Mobile. It looks like the carrier was willing to slice its profit margins on individual accounts in order to get the distribution from Wal-Mart.
Wal-Mart will offer five phones with the plan starting at $35; in some cases, they'll be slightly cheaper than their counterparts on other networks and plans. For example, T-Mobile sells the Motorola Cliq XT for $349 without a contract, but it will just cost $249 from Wal-Mart.