Truphone is a leading VoIP service provider for mobile phones in the sense that has been the first to provide a VoIP application for the iPhone and for the Nexus One. Truphone allows Android users to make free calls to other Truphone users over Wi-Fi, with cheap rates otherwise. It also allows the user to make partly-VoIP calls over their GSM (cellular) network, through its Truphone Local plan. This allows the user to use the cheap service anywhere outside Wi-Fi. Note that Truphone on Android does not support 3G so far.
2. SkypeUsing Skype's application for Android, which you can download from there on your phone itself, you can make free Skype-to-Skype calls worldwide, over 3G and Wi-Fi. However, t the time I am writing this, users in the US aren't able to make 3G calls.
3. VoxofonVoxofon is a cool and easy way to use VoIP on your Android and at the same time save money on international calls. You don’t need Wi-Fi or 3G – you can make calls through your GSM network itself. Here is how it works. You enter any international number and click to call. Before the call starts, the service determines the cheapest route and you are shown what it will cost. The cost will be the local cost plus Voxofon’s cost, which is no more than a couple of cents per minute.
4. FringFring is another VoIP service that works the common way – free calls to other Fring contacts over EDGE, Wi-Fi or 3G, and paid calls to other phones. Fring also allows you to communicate with people on other networks like Skype, Google Talk etc.
5. RaketuYet another of the common mobile VoIP applications, with the possibility of communicating to contacts on other networks like Skype, Yahoo IM etc. Raketu also has many different ways of starting a call, 8 in all, as it says on its site.
6. RF.comRF.com is first known as a service that supercharges the iPhone with the ability of making cheap VoIP calls through the GSM network. It also allows SIP URI calls and calls to Voice over IM Services (such as Skype, Google Talk, MSN Messenger and Yahoo! Messenger), and other IP-based voice services. Now RF.com also works with some models of Android phones, including the G1.
7. PhoneGnomePhoneGnome is one of these box-based VoIP services that ship you a box through which all magic works. The add-on device can allow you to use your mobile phone to make cheap international calls, any mobile phone, including the Android.
MO-Call for Android works on many Android phones and can work even without an Internet connection on the mobile device. The cheap VoIP calls may be routed to the IP network, wherre VoIP will come into play, through the local GSM network.