Dependant on where you are trying to ring, this might work for you. I'll assume UK landlines.
Look at the various voip software, I use voipstunt so that will be the example.
Go to
www.voipstunt.com and download their software.
Open an account with them by placing €11.60 (about £8.12p) of which €10 (£7) will be usable credit.
This will be valid for 120 days.
Set up the software so that your home number is in the "Direct callback nr" box.
In the box at the bottom enter your target number. Land only because mobiles are too much.
Press the green button.
Your landline will ring. Pick it up and you will hear a ringtone as it tries to connect you with the target.
Upon connection your account will be debited by €0.03 (2.1p) inc all taxes.
You can now talk for up to an hour before the system cuts you off. You can redial if you wish.
There are several countries, including their mobiles, that are free (+ connection fee) eg USA land & mobile.
Credit remains for 120 days and is lost if you do not top up within 5 days of termination. If you top up in time, all remaining credit is kept + the top up.
So you can connect for 2.1p doing it this way, or for free if you want to go through the computer as a voip call.