Telecoms regulator Ofcom is introducing clearer charges for numbers starting 084, 087, 09 and 118.
These so-called 'service numbers' are used for finding out information, contacting a business or helpline, or using competition, directory-enquiry, entertainment and voting services.
Every year, callers in the UK spend a total of 250m hours calling these service numbers, spending around £900m between them, according to Ofcom research, but until now, callers to these numbers have not generally been told by the service provider how much they will be charged.
The change also means that calls made by mobile to freephone numbers will also become free in practice and not just name, the regulator said on Thursday.
Until now, callers to these numbers have not been told by the service provider how much they will be charged. They have usually been informed that they "may" be charged for the call - they have just not been told by how much.
Sharon White, Ofcom chief executive, said: "Next month we'll see the biggest changes to telephone calls in over a decade. Together we spend around £900 million a year on these calls, so it's important that people understand the cost before they pick up the phone.
"From 1 July, callers will be able to see how much they're paying and where their money is going. The website ukcalling.info has more information on the changes, and what they mean for you."
From 1 July, Ofcom said, "charges for service numbers will be made up of an 'access charge' going to the phone company" in addition to a "service charge" set by the company or organisation being called.
But once again Ofcom has ducked the issue of dealing with the most contentious part of the whole system - before making the call the user may only be told that they might accrue a charge. As Ofcom puts it: "Phone companies will be responsible for setting their access charge, making it clear to consumers on their bills and informing new customers of the charge when they sign up to a contract."
Ofcom admitted: "We are not in a position to set out in detail how [the telecoms suppliers] format and display the information that they put out to customers as that is not in our remit.
"But we do continue to work with the industry to improve how it communicates with customers."
Currently, callers are given information such as:
"Calls cost xp per minute from a BT landline. Calls may vary from other landlines and calls from mobiles may cost considerably more."
Under the new system, the cost of calls will be explained in a simpler format such as:
"Calls cost xp per minute, plus your phone company's access charge."
Also from next month Freephone numbers (beginning 0800 and 0808) will become free for consumers calling from mobile phones, just as they generally are from landlines.
The telecoms regulator is also rolling out a strengthened code of practice on broadband speeds, allowing customers to exit a contract should speeds fall below acceptable levels, and new processes to make switching broadband and landline providers easier.