Nokia smartphones are not cheap, especially the multitasking on which also has WI-FI and 3G, better for making VoIP calls. If you have purchase such phone and you just end up by making and receiving regular calls then I bet you are not using 5% of your phone features. These Nokia phones are quite capable and the people who know it they use it as a primary business of communication. Many use it to make cheap national and international calls using technology like VoIP.
Making calls using internet (Internet calling or VoIP calling) is not so old technique but it becomes so popular that some times it looks like it was always there. Now the cellphone industries are concentrating in VoIP technology to make their device more VoIP friendly. It might be possible at future when internet speed will increase and mobile VoIP becomes more popular and that time the calling cost will be cheaper then you can imagine no matter it will be national or international calls.
Nokia phones are best in majority if you compare to any other brand. Nokia E series and N series phones are VoIP capable phones
. If you talk about E series they are business phones same time they also support VoIP features and on other then Nokia N series which his mostly multimedia phones with good sound and camera but also supports VoIP callings. Most of the Nokia phone comes with pre installed application to make VoIP calls but if not then you can easy find a list of supportive VoIP service provider application on internet.
The other thing is SIP setting, either you go for default one and if its not working then you can find different types of SIP setting on internet for your specific Nokia handset.