The charger which comes with the iPhone does NOT have a voltage converter. The charger is only to make the UBS connection to the power source, which is 110v. If you plug in a socket adapter to the charging device without a voltage converter into a socket with 220v current, you will likely have very undesirable results. Apple did thie for a reason; they want to sell you their international converter kit which contians socket adpaters for most places in the world, as well as a voltage converter. we don'tg remember what the cost was, but it wasn't expensive. Obviously, this can be used with ANY Apple device, computers, iPads, etc., with no problems. If you purchase the Apple universal converter kit, you will not need your charger connection, as this kit comes with both connecting cord, UBS connection and transformer. We recommend it, if you are taking your iPhone overseas.
For simple socket connectors, we recommend that you purchase a set of socket adapters. You can purchase them at Radio Shack, any of the electronic stors, or even wait until you go the airport and get one at Brookstone, or any other of the concessions you'll find. We use these adapters to plug our camera charges into the local sockets. We don't need transformers for these, because they are dual volatage, as they all are. We carry a hair dryer, however, we have found, with the exception of Africa, that hair dryers are provided, all using the local voltage. that seems to be becoming the norm, but we still carry our own, which is a dual voltage model just in case.