O2, Three and Vodafone have joined EE in announcing price rises for pay-monthly mobile customers this year, MoneySavingExpert.com can reveal.

All four major networks have now confirmed they intend to increase prices in line with the Retail Prices Index (RPI) measure of inflation, published monthly by the Office for National Statistics. Here's what they've told us is happening to pay-monthly contract prices:

  • EE is increasing prices from 30 March by 4.1% (December's RPI figure)
  • O2 is increasing prices in April by 4% (January's RPI figure)
  • Three is increasing prices in May by 4% (January's RPI figure)
  • Vodafone is increasing prices in April based on March's RPI figure

For help on cutting the cost of your mobile bill, see our 30+ Cheap Mobile Tips.

I'm mid-contract – can I leave penalty-free?

Unfortunately you almost certainly won't be able to. Mobile firms CAN increase prices mid-contract in line with inflation without you being able to leave penalty-free, as long as they include a warning about this in their terms and conditions. Three, EE and O2 do, and Vodafone does for contracts taken out on or after 5 May 2016.

There is a rule set by telecoms regulator Ofcom that means you can escape your contract penalty-free if you can successfully prove you've suffered "material detriment" as a result of a price increase – though it would be very hard to prove an RPI increase had caused this.

Make sure you note down when your contract is due to end, and start looking for new deals about a month before.

What if I'm out of contract?

Regardless of price increases, if you're out of your minimum contract term you can leave without paying any penalty, and there's a good chance you can save by switching to a better deal – especially if your original contract deal involved paying for a handset.

Most should NEVER pay over £10/month for mobile use, particularly given two-thirds of mobile users consume less than 3GB/month. See our Mobiles section and Cheap Sim-only Deals guide for full help on finding a cheaper deal elsewhere.

Alternatively, if you're willing to stick with your network, this is a chance to haggle a better deal – especially as you have the right to leave penalty-free (again you don't need to wait for the price rise).

See our Mobile Haggling guide for detailed tips, but here are a few to get you started...

  • Benchmark the best deal elsewhere so you ask for a realistic discount.
  • Get through to the retentions (sometimes called disconnections) department. They have the most power to slash costs, as their job is to keep you.
  • Use charm and be friendly. Aggression or anger will just put their back up.
  • Don't panic if they call your bluff and say they'll disconnect you.

Mid-contract price rises 'an occupational hazard'

Guy Anker, managing editor of MoneySavingExpert.com, said: "Price rises such as these from O2, Three, Vodafone and EE are an occupational hazard for most mobile users, as they happen every year.

"While customers in contract are normally still tied in after a hike, any rise should act as a timely trigger for anyone free to move to save £100s by finding a better deal, given Sim prices have dived over recent years. Those on legacy tariffs are likely paying lots more than the best deals."

What do the networks say?

An EE spokesperson said: "Like many service providers, our pay-monthly plans increase by RPI annually, and this year customers on our most popular plan will typically see an increase of 85p a month. We're currently contacting our customers to remind them this will take effect from 30 March."

An O2 spokesperson said: "We know that our customers want transparency and control over their monthly bills and, importantly, don't want to be forced to pay for a phone they already own. By splitting the airtime and device plan, we've helped our O2 Refresh customers avoid paying millions of pounds."

A spokesperson for Three said: "This year, our customers will see an increase of 4% – for example a Three customer currently paying £20 per month will see an increase of 80p per month. We plan to start introducing this during May 2018 and will be getting in touch with impacted customers, to let them know of this change and how this will affect them directly.

A Vodafone spokesperson said: "All new pay-monthly contracts taken out on or after 5 May 2016 have an annual price adjustment in line with the RPI. For consumer contracts, we use the RPI figure published by the Office for National Statistics in March and apply the change in April each year, from 2017."

What about the smaller networks?

We've asked BT, Giffgaff, Plusnet and Virgin Media whether they will also increase customers' bills in line with RPI.

Virgin Media and Giffgaff have told us they are not currently planning to raise prices. Plusnet has said RPI price rises do not apply to its deals, as it offers 30 day rolling contracts. BT told us it does not comment on future plans.