Hoiio

How it works: Its callback feature converts outgoing calls to incoming ones, which are free for local calls. Once it is installed, users can make calls as per normal - via the contacts list or keypad.

Cost: 3.8 cents a minute for calls, 8.8 cents per SMS to any country.

To use: Download from website or from app stores such as the iPhone or Android Marketplace.

Pfingo Bounce and Talk by StarHub

How it works: Pfingo Bounce works on the same callback feature as Hoiio, while Talk uses your mobile data to make calls.

Cost: Free for the basic version, pay if you want more features. IDD rates are at 2 cents a minute. 10 cents per SMS to any country.

Nimbuzz

How it works: It offers free calls to other Nimbuzz users by using your mobile data connection. A plus: You can connect to your MSN, Facebook and Google chat friends also.

Cost: Free, but pay for its premium plan which allows calls to non-Nimbuzz users and international calls at low rates.

To use: Key in your mobile phone number on its website and a download link will be sent to you via text message.

All applications can only be downloaded on smartphones such as the iPhone, Blackberry or any phone working on Windows Mobile.

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