VOIP is a way to make exceedingly cheap if not free phone calls, Most of the current smart phones have mobile voip apps to download and even the ipad for voip mobile apps.

You can use an

Iphone to access voip apps
HTC for voip phone calls
Android voip mobile apps
Nokia voip apps
Samsung moile voip phone calls

I could keep going but you will get bored have a look through my list of top voip mobile app providers.

Voip can be accessed through your handsets 3g connection or through wifi.

Below is a list of mobile voip apps on the market

Voip apps

Nimbuzz

Support for voip mobile phone calls and messaging Skype – A well know voip provider they can offer cheap phone calls through your handset.

Beejive

AIM Mobile Chat

Fring – Connects with Skype, MSN Messenger, ICQ and Google Talk from your iPhone giving you limitless possibilities on making cheap phone calls.

Truphone

Vonage

A long standing provider with a good reputation in voip. Jajah

Yahoo! Mobile Chat

Vopium