Mobile phone contracts are big business in the US, and are frequently incentivized by offering free or cheaper phones, like both Walmart and T-Mobile have done with the Lumia 710 from time to time. For the big phones, which regularly pass $500 in contractless cost, the subsidy of a contract is often the only way to get a good deal on a phone. Ordinarily the 710 is offered for $350 off contract, being a mid-range phone, but according to My Nokia Blog, you can get it for even cheaper now.
post shows that T-Mobile retail stores are offering a contractless phone for only $200, a typical on
-contract price for high end phones. The purchase of a plan is required, but the plan can be as short as you like, so a month of 4G service tacks on $50 to that. You can of course continue the pre-paid plan at your leisure or stop after the month is up. You'll need to check with your local store and ensure they're aware of the price change, but their systems list it as a permanent deal, and a good deal it is if you can't abide by contracts.
[My Nokia Blog