If you intend to considerably cut down the cost of your mobile calls, here is a list of VoIP services that can allow you to cut down your mobile communication costs to the cheapest it can be so far. You only have to select the right service tailored to your needs, mobile phone type and model, connectivity, etc.
Yeigo is here to end paid-for mobile communication as you know it. It is a free software application that can be installed on mobile phones for calls and messages to any mobile or landline anywhere in the world. Calls are free to other mobiles using Yeigo, anywhere they can be in the world. Yeigo works on most recent mobile phones on the market. To use Yeigo, just like many of the applications of its like in this list, you need to have a data connection like Wi-Fi, 3G, GPRS, etc. Read more on Yeigo here
Fring is also a free application to be installed on a mobile phone for calls and messages. Calls to other Fring others are free, and are paid at cheap rates to landline and mobile networks. The cell phone models on which Fring works is more limited than for Yeigo. However, Fring users can communicate with users of other instant messaging service like Skype, MSN Messenger, ICQ, Google Talk, SIP, Twitter, AIM, Yahoo etc. Fring also requires a data service plan like WiFi, 3G, GPRS etc. Read more on Fring here
By installing the Truphone software on your mobile phone, you can have your mobile phones routed through the Internet,and make free calls to other Truphone users. Calls to plain mobile and landline phones are cheap. Truphone allows you to make calls through Wi-Fi hotspots and your GSM network, which means you can use it really anywhere. It focuses mainly on high-end phone models like the iPhone, BlackBerry devices, Nokia E and N series etc.
Vopium is a mobile VoIP service that offers cheap international calls through GSM and VoIP, without necessarily having a data plan (GPRS, 3G etc.) or Wi-Fi connection. If you do have any of the latter, you can make free calls to other users using the same networks. Vopium also offers new users 30 minutes free calls and 100 free SMS for trial.
is a list of VoIP services that work on Apple's iPhone.
is a list of VoIP services that work on Blackberry machines.
Packet8's MobileTalk is a pioneering service in the field of Mobile VoIP and is interesting for people who spend heavily on international calls. The rates are cheaper than for fixed VoIP. However, only US residents can benefit from it now. The service is different from other services on this list, in that it is hardware-based. It works through the GSM service, which means you don't need a data service like WiFi or 3G or GPRS etc. However, local calls are not as cheap as you would expect with mobile VoIP, so the service is ideal only for heavy international callers. Read more on Packet's MobileTalk here
Jaxtr is a nice and completely free service that allows you to make phone calls to and from fixed or mobile phones. You first need to create an account and submit a phone number through which you can be contacted. Then you can call other people who have done the same. The first time, you need to call them through the web interface or jaxtr, then, once you have saved the virtual number of the person on your phone, you can call them from it the next time. International calls are also supported. Note that the phone number you submit will not be seen by other people, but a virtual number will be used instead, assigned by jaxtr.
Yackie Mobile is a pioneering new type of service in the field of mobile VoIP - it offers VoIP on a SIM card. This eliminates the need for data plans or WiFi connections. You simply have to buy and insert the SIM card in your mobile phone, register for the VoIP service and start using it. The rates are standard cheap VoIP rates; and the international rates are quite advantageous.
With Talkety, there is no software to download and install. You don't need a computer for calls, but you do need one for registration, payment and recording numbers. Yes I said payment, because the service is not free. You can call anywhere on any kind of telephone anywhere in the whole world. They also have a Pro service. To use the service, you enter the numbers, the phone rings and the talkers are connected.