If, like me, you’re a BT broadband customer, you may be slightly puzzled by what turned up in the post this morning.

The letter I received actually appears to be offering something for nothing – in fact, less than nothing.

It says I can pay £2 less a month and make internet and phone call savings plus have a free “hub phone” and “home hub”, whatever they are. (Yes, I know I should have been paying attention to the adverts with that nice bloke from Love Actually).

I’ve read the letter twice and still haven’t spotted the catch.

Can it be that BT is cutting prices in a bid to retain customers? Or is something more sinister going on?

If anyone has any thoughts, please let me know.

Do you know how much you’re being charged each time you dial an 0870 number?

Thought not.

Consumers’ organisation Which? says most people don’t realise how badly they’re being ripped off when they call this code.

Organisations that use 0845, 0844 and the even more expensive 0870 and 0871 numbers get to share the profits with the phone service provider, so it’s in their interests to keep you on the line for as long as possible.

No wonder these ‘revenue sharing’ numbers are so popular with so-called customer service departments and helplines provided by everyone from broadband and power companies to government agencies.

Some banks, including Alliance & Leicester and Lloyds TSB, even use 0870 lines to offer advice to customers with debt problems.

A ten-minute daytime call from a BT landline to a standard geographically-based number (these begin 01 or 02) could cost as little as 3p, but the same call could be about 80p to an 0870 number.

And that soon adds up to a very tidy profit.

The Department for Work and Pensions has admitted it made £268,000 last year from 0845 hotlines to advise people on low incomes about benefit and winter fuel payments.

Which? editor Neil Fowler says: ‘Revenue sharing is a stealth tax of the worst kind.

‘Tales of customers hanging on for ages at huge expense when they are trying to place an order – or even make a complaint – are numerous.’

But there is a way to avoid the ‘revenue sharing’ rip off.

Whenever you need to dial a firm that gives out an 0845, 0844, 0870 or 0871 number, simply log on to website Say No to 0870 to find a geographically-based alternative that charges standard rates.

Finally, a financial initiative deserving of praise (although probably not by the retailers whose profits will suffer as a result).

If you want to save money at some of your favourite shops, there’s actually a website that lists all the latest online discount and promotional codes.

So whether you’re heading for Amazon, B&Q, John Lewis, White Stuff or any one of dozens of others, it might be worth stopping off here first.