All Apple products tend to come with an adapter that works with 110-240 V. So just change the prong part of your adapter (if it's the same brick type than the other products, maybe use a spare of your iPod or other charger for it).
It's odd that it isn't specifically mentioned in
tech specs or
manual, but it should be mentioned somewhere. In the box perhaps? Or in the charger itself, there has to be a notification of the supported voltage. I would be very surprised if it would not be 110-240 autoswitching, considering the phones are for a very mobile audience.