Skype now has a beta version for the N95:
http://www.skype.com/download/skype/mobile/choose/downloading/?downloadId=56&selectedDevice=nokia_n95
Nokia provides an excellent tutorial on how to use and configure SIP-based VoIP on your Nokia:
http://europe.nokia.com/A4745405
Here is the Nokia N95 85 User Guide in PDF:
http://nds1.nokia.com/files/support/nam/phones/guides/N95-4_US_en.PDF
Page 117 explains how to configure for SIP based VoIP services.
To use with SIP based VoIP services, you will need an account with a SIP (Session Initiation Protocol) based service providers like CallCentric, InPhonex, Les.net, Voip.ms, etc.
These services are BYOD (bring your own device) and only pay-as-you-go prepaid calling (no contracts). You can get incoming phone numbers for your area code to receive incoming calls to your VoiP enabled device.
I use CallCentric and InPhonex with my Linksys VoIP adapter as my VoIP service providers. I also use them with a Softphone on my PC for making Internet calls.