But it is the humble home phone line that often gets overlooked, particularly as we all rely increasingly on mobiles for the majority of our calls. Indeed, recent research shows that a third of households have not changed their home phone provider in over 5 years. The net result is that the majority of households are sitting on a big potential savings without even knowing it.

Home phone costs consist of the line rental (paid monthly) and the cost of the call plan on top. There is not much variation in the cost of line rental, which varies from ?10.50 to ?11.25 per month depending on your home phone supplier. But there is a huge potential difference in the cost of the calls depending on which call plan you choose from which supplier, relative to where you make the majority of your calls.

Identifying the exact potential cost saving for a household is complex as it is dependent on the household's unique pattern of calls. So for simplicity we have grouped households into categories to determine a likely potential cost saving.

Busy family making regular daytime calls during the week

Let's assume that the family regularly makes local and national calls during the day, as well as regular calls to mobiles.

In this example there are big savings to be had by getting a call plan with all inclusive daytime calls, because if you make calls during the day without an inclusive talk plan, you will be paying through the nose.

For example, BT charge 4.5p per minute for daytime calls, so a family spending 20 minutes on the phone per day to landlines will be spending ?18 per month on national calls alone.

If for example they are spending another 20 minutes per day on calls to mobiles (which BT charge at 12p per minute), this would add up to another ?50 per month, making a total of ?68 per month excluding line rental! In contrast the pick of the anytime call plans are listed below.

Sky Talk Anytime (?5 per month for Sky TV customers)

This package is very good value and gives you unlimited free national daytime calls, plus free calls to 20 international destinations including France and the US. And importantly calls to mobiles would be just 9p per minute. So instead of paying ?68 per month, the family would pay a total of ?41 per month (excluding line rental) and benefit from the free international calls ? making a saving of about ?27 per month or ?324 per year.

TalkTalk UK Anytime

The TalkTalk package is another great value plan. For ?4.49 per month you get free daytime calls (this rises to ?5.49 per month after 12 months). Calls to mobiles are 12p per minute and you also pay for calls to international destinations. But on this basis you would still expect to save about ?186 per year (?15.50 per month)

BT Unlimited Anytime Plan

This plan costs ?4.95 per month for free daytime, evening and weekend calls. Calls to mobile cost 12.5p per minute and BT's standard international call charges apply. But by switching to this plan, the family would still save ?13 per month or ?157 per year.

A major drawback of the BT package is that it ropes you in to a 12 month ?renewable contract? which automatically gets extended to an additional twelve months, after the completion of the initial 12.