All the carriers including MVNO's entice you with their international plans. VoIP is the best viable option and much cheaper.
If you have android or IOs, you can download one of the many many apps where you can use your phone overseas for cents on the dollar and you pre-pay for the minutes you use and can research the country you are travelling to and the rates. I have used this and it works very very well. No need to get a local SIM card or use your local US carriers outrageous international roaming rates.
Using VOIP implies that you will have access to WiFi, which, depending on where you are, you might not. Granted, if you have access to free or cheap WIFI that would be the best option, but not everyone travelling abroad has that option.
International roaming is a rip-off on most carriers
If you have a roaming capable phone, it is much less expensive to have your phone unlocked and use a local carriers SIM card and service.
T-Mobile is the only US carrier who has this right-- they offer prices competitive to local carriers for roaming and calling home, and even throw in data (albeit 2G).
the only problem with using a local carriers sim is that your device would have to be unlocked and most people are within contract on that phone, so they dont have that option
T-Mobile can offer lower prices on international roaming only because they ARE an international carrier to begin with, and thus when overseas the phone is actually on a network owned by the same company, from T-Mobile to another Deutsche Telecom carri...