Viber - making VoIP calling simpler

Lots of apps do cool stuff but can add a layer of complexity by requiring registration and a username. Viber cuts your call costs by providing free calling between iPhone users with none of the complication of a new number or username - it simply uses your existing mobile number. When you make a call, instead of using the iPhone Contacts app, you use the Viber app which is synced with your contacts. If the person you're calling uses Viber, an icon is displayed next to their name and the call is free (if you pay for 3G data then any usual data charges will apply); if they don't, the call will be routed as usual via your mobile service.

Viber uses WiFi or 3G data depending on what's available and call quality is excellent. If Viber isn't running when you receive a call, you receive a push message on your screen to alert you to the call. Just tap on the message to answer the call.

Setup is simple; just launch the app, enter your iPhone number and you'll be sent a code by SMS to confirm it's your number. When I installed Viber I was impressed to see that several of my contacts were already using Viber. When new friends join, you get an alert.

Any drawbacks? No voicemail so if the person you're calling isn't available you'll need to make a regular call to them to leave a message.

Viber has got more good stuff in the pipeline - free SMS is coming later this month, followed by an Android app and later a BlackBerry app.

You can follow @Viber on Twitter.