It's no secret that making calls on your iPhone while traveling abroad outside your home country can be expensive. Some people have faced bills of hundreds or even thousands of extra dollars! Using your data plan when on the road can be outrageously expensive too. Luckily, there are a few solutions. First, look into an international calling plan. While this certainly will not be cheap, it's better than the normal rates. A better solution is Skype for iPhone which will allow you to place VOIP calls on the iPhone. It's not free, but the rates are amazingly cheap compared to a traditional phone company. One note is that you will only be able to use it while you are connected to the internet via Wifi.
You should also try to avoid using your 3G or Edge Internet connectivity when traveling abroad since it can be expensive too. Be careful because some phones may be configured to automatically access the Internet and may cost you money without you doing anything. You can turn this off, or the truly paranoid will leave the phone in airplane mode when traveling abroad in order to make sure no data is used. In order to get internet access, you can usually find an inexpensive or free Wifi wireless network and connect that way. This won't cost you anything on your monthly phone bill and is the best way to check your email when traveling internationally. By taking this advice, you can avoid a surprisingly large bill when you return home!