With Voip you can talk to your friends and business contacts,without adding talk time on your mobile phone bill. Calling using VoIP with your phone feels and sounds just like a regular phone call. All you need is a phone with VoIP, a VoIP service provider, and a connection to the internet.Exactly how you use VoIP depends on the service you’re using. You can usually call someone on a computer or VoIP phone number without any extra cost. If you call a land-line or mobile phone, however, your VoIP signal must be converted to a regular telephone signal, that usually involves a subscription service.

Here are some ways you can use VoIP on your phone:

At home or at the office
If you use a WLAN for your home or work network and have a service agreement with a SIP VoIP service provider, you can use your phone to make cheap or free VoIP calls. There’s no need to sit in front of your computer or use any devices other than your phone. The best part is, you can be reached conveniently by all of your callers at one number, with one device.

Out on the town
You can make VoIP calls from your favorite restaurant, for example. Your mobile or broadband service provider may have WLAN “hotspots”– wireless internet access points – around town. Some restaurants and school campuses also have their own hotspots available for their customers and students, and you may even find a public WLAN hotspot with free access for everyone.

What Nokia devices use it?br />
Nokia E90
Nokia E70
Nokia E65
Nokia E61i
Nokia E61
Nokia E60
Nokia E51
Nokia N95 8GB
Nokia N95
Nokia N810 Internet Tablet
Nokia N800 Internet Tablet
Nokia N82
Nokia N81 8GB
Nokia N81
Nokia N80 Internet Edition
Nokia 770 Internet Tablet

Source: NOKIA Phone with VOIP Features