The Nokia 2720 flip phone can be purchased new and unlocked from several websites. Two reputable websites include Cell2Get.com and ElectronicsForce.com. Since this phone was released in 2009, it is becoming more difficult to find and prices can be volatile.
These phones also commonly appear on marketplace websites such as eBay.com, Bonanza.com, and eCrater.com. You are unlikely to find a Nokia 2720 in a physical store, unless they specialize in used and refurbished electronics.
Prices, as of 2015, are in the range of $20 for a used unit, $40 for a refurbished unit, and $80+ for a new-in-box (NIB) unit.