two ways to do that - in H/W or in S/W
H/W - plug a voip box into your router & plug a 'ph into that
- I usually suggest to use a cordless 'ph
- the advantage of this, is that you don't need to power_up your PC, to make any calls.
S/W - usually skype, - although there are others.
- can be a video or audio call
- requires the S/W to be installed onto your PC, - so your PC needs to be up & running, to make any calls.
both ways, have "cheap calls" that can be made, to any type of 'ph
But:- both ways DO require a INTERNET connection - as that is what VOIP - is.
any other way, would require, say a smartphone, - with skype or similar installed.
But - again - it's a data connection - that is required - for the VOIP to succeed.
so, basically - you will need a Internet connection .. ..