The iPhone 4s is a great choice for a smartphone, but finding an good price on one without a contract may prove to be a challenge. If you're not picky about the carrier you can get one (for $99) from MacMall below made for the Verizon network;
http://www.macmall.com/p/Verizon-Apple-iPhone-Cellular-Telephony/product...
Macmall is a great place to buy older Apple equipment outside the regular Apple Store, and is an Authorized Apple Reseller (availability on that offer is limited to Verizon contracts, and there is not always stock). If you are patient, you can create the order and wait to see if the stock is replenished. Fortunately there are several other online stores. Using an iPhone with a local carrier such as Verizon is an option, particularly if you can purchase the phone from a reputable store with current stock, such as Amazon ($289), see below;
If you do not plan on going with a local carrier at all, you're going to want a completely "unlocked" phone. The best option currently is below from Amazon ($350) and is under the "used" section;