PHONE callers angry at being overcharged by 0870-coded numbers are increasingly likely to boycott firms using them, warn experts.

Britons collectively spend £59 million phoning 0870 numbers at nearly 8p per minute.

Many are ignorant of the higher cost of calling compared with up to 3p per minute when calling normal fixed line numbers.

For 12 months regulator Ofcom has been warning businesses of new regulations which will force them to declare in advance how much it will cost people to dial 0870 numbers.

But "greedy or badly advised local companies are still being sold 0870 numbers - many will be in for an expensive shock," warned Andrew Holford of Wimborne-based telephony advisers CommerceCall.

"In the Bournemouth conurbation, business from solicitors and insurance companies to high street travel companies are increasingly using 0870 numbers.

"Unlike geographic numbers, all 08-prefixed numbers can be linked to many useful services, such as over-the-phone payment systems, but the market is plagued by mis-selling, ignorance or simple greed.

"To call them costs a huge amount more than if we call 0844 or 0845 so why do they do it? Profit or ignorance?"

New regulations are expected after spring 2006: "Given the publicity that will undoubtedly arise when the change happens, there will be very few companies who will want to risk their reputation by continuing to use 0870 numbers.

"Businesses will have little option but to change their number to different and cheaper-to-call 0844 or 0845 numbers and - to avoid damaging their reputation - must consider the change now," said Mr Holford.