fring (all mobiles)

You can easily use VOIP on the iPhone over WiFi with no restrictions, allowing you to save money or your plan minutes by using the much cheaper VOIP rates. The iPod is also capable of making the very same calls with VOIP as long as you use a microphone or a headset with a microphone, such as the one that comes with the iPhone.

You should also be able to place VOIP calls over 3G if your cell phone provider allows it. In Canada, Rogers and Fido allow such calls.

You may use the free fring which allows even video calls.

There are numerous other applications that you can use. We recommend the free Siphon or the excellent Acrobits Softphone at $7.99.