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.
Using 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.
Voxofon 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.
RF.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.
Fring 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.
Yet 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.
PhoneGnome 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.
Android users using Vonage can extend to the Vonage Mobile service and install the application for Android on their phones. This will allow them to make calls over Wi-Fi and GSM, with cheap international rates in over 60 countries. Calls can be made only on AT&T, T-Mobile, Verizon and Sprint network.
10. Jajah Mobile Web
Jajah is a web-based VoIP service. It doesn’t actually have a VoIP application for the Android – it doesn’t have any for any phone really, because its service is accessed only through the web, and practically most of the phones out there with web-connecting capability will be able to use it to place calls over Wi-Fi or 3G.
11. Native SIP Clients
More skilled VoIP users can use SIP clients that are native to the Android platform to make their calls through SIP. These are merely applications that allow you to use VoIP that support SIP and that do not have a (good) VoIP application for Android. Examples of such applications are the SIPdroid client, SIPez, the Skuku client etc.