Types of Voice Calling Services
There are two broad categories of voice calling services.
(a) Those that require you to download an application or to have it pre-installed on your mobile phone. Types (1), (2) and (3) below are in this catgory.
(b) Those that don't require any application on the phone itself but make use of regular mobile phone features such as address books and web browsing. You can use the phone as it is. Types (4), (5) are in this category. Type (6) requires a new SIM card.
The way that calls are made and connections set-up has a strong bearing on the advantages and disadvantages of a particular service and its use. This is often not clear from the information on providers' websites. Brief summaries of how calls are made are given below with links to more detailed tutorials.
We also cover some providers that don't neatly fall into the above categories but who represent innovative and related mobile services.
Mobile Phone Applications
(1) Mobile VoIP
Mobile VoIP systems run VoIP software on your mobile phone and use either a WiFI network or your mobile phone's data connection to link to the wider IP network.
Mobile VoIP systems can meet all your mobile calling needs not just international calls. You also have free calls between online users of the same service like Skype.
Mobile VoIP services can use a WiFi wireless local area network (as you may have at home or in the office to connect computers together), or a WiFi public hotspot (as you might find in a coffee shop, hotel or airport lounge), or your mobile phone's data connection to connect to the Internet and communicate with the wider world.
Mobile VoIP over WiFi Access
See diagram (pdf) of Mobile VoIP over WiFi and detailed explanation here. See issues here.
Mobile VoIP over Mobile 3G Cellular Data
See diagram (pdf) of Mobile VoIP over cellular data and detailed explanation here. See issues here.
Integrated or Stand-Alone Mobile VoIP
Mobile phones are available with basic VoIP functionality built-in by the manufacturer. In these cases the service may provide just settings for your mobile which can be downloaded and automatically installed or the settings and an application which makes using the VoIP service easier.
Stand-Alone Mobile VoIP services provide a downloadable application which includes all the necessary VoIP functionality.
For Mobile VoIP you need a dual-mode 3G smartphone. Dual-mode so it can use both WiFi and mobile cellular wireless.
(2) Call-Back
The application on your mobile uses your mobile's data channel to signal the service to set-up the call. See diagram (pdf) and detailed explanation here.
Call-Back - SMS-Activated (may or may not have application on phone)
This can be used from any mobile phone. You or the application on your phone sends an SMS in a specified format containing the number to be called to a server. The server initiates a call-back call set-up process. See details (pdf) here.
(3) Call-Through
Call-through is usually a time consuming two-stage process. You dial a local number, enter a PIN and then dial another number, the number you want to call. The mobile applications covered here are seamless.
On selecting the contact you want to call the latest mobile services will automatically call an appropriate local number and put you through to your contact. See details (pdf) here.
Call-through is also able to deliver other kinds of connections including mobile access to your Skype account so that you can use Skype from your mobile phone. See details (pdf) here.
No Application Needed on Mobile Phone
(4) Web-based Calling
The service provides a website designed to work well on mobile phone displays and mobile web browsers. You use your mobile’s data connection and browser to visit the website where you initiate the call by selecting or providing the number you want to call. The service makes a call to your contact at the same time calling back to you and connects the two calls together when both you and your party have answered.
(5) Alias Numbers
Alias Numbers are a form of Call-Through system. You are allocated a local phone number for each international contact that you regularly call. The local number can be stored in your mobile phone address book for that contact and you simply select that contact in your address book to be connected to them. You make calls in the normal way and you do not have to change your calling behaviour or procedure as you do with two-stage call-through systems. See details (pdf) here.
Alias Numbers are very useful if you regularly make international calls to the same people; business associates or family, for example. There may be a limit to the number of numbers you can have.
(6) International SIM Cards
Providers of these International SIM cards have a roaming agreement with a local mobile service provider in each country so that the SIM card is recognised as a "local" card in that country and calls made in that country are treated as local calls. Calls made outside the country are international calls.
This is in contrast to certain "international" SIM cards that have a number in a country that charges very high termination rates to incoming calls but low rates for forwarding calls to roaming SIMs.
Consequently, the SIM card user in this case doesn't pay the usually high cost of having a call forwarded to his roaming SIM card. The high cost part of the call is transferred to the person making the call who has to call a number in a country like Latvia or Estonia and pay the high termination rates associated with it. Your contacts will also find it odd having to call a number in an unusual country rather than you normal number.