I don't have a land line at home, so when I have to call companies (such as virgin media etc) I am charged for the privilege (if you can call it that!).
Many mobile operators charge you by the minute to call 0800 numbers (GiffGaff do not charge!) which are usually free to call from a land line. If you speak with your mobile operator, you can get these numbers included with your phone package for an extra charge or USE MY TIPS BELOW!
Here are some methods in the past that I have used to use my inclusive mobile minutes and call for free:
********* Calls to 0800 numbers only *********
SKYPE (Mobile App)
You can download Skype for free for IOS, Android, Windows Phone and PC/Laptops. Skype will allow you to use wifi/3G to dial 0800 numbers for free!
Also, try http://www.0800buster.co.uk/, which is a number you can dial from landlines/mobiles to get free calls to any premium rate number (as far as I can tell). Thanks to olilovespies!
Three have announced that calls to 0800 numbers will be free on their network.
********* Calls to 0870, 0845 and 0800 numbers *********
SAY NO TO 0870
There is a very handy website called "say no to 0870" (click deal link) which lists alternative numbers for big companies. You can type in the premium rate number or the company name and it tells you all of the alternative free or local rate numbers that are available.
GLOBAL DIAL IN NUMBERS
Some companies also have global dial in numbers which start with +44 which is the UK country code. If you replace this with a zero, it is a local rate number and will be included within your mobile minutes. You can use localphone.com to find the UK number for each of these (thanks to mjunaid106).
WEQ4U Mobile App
Also worth trying is WeQ4U http://www.weq4u.co.uk/ which also has apps for IPhone and Android. It works on both wi-fi and 3G. Thanks to Daddio2