She said: "Too many people are put off by the hassle of switching mobile provider".
Vodafone, which has been slammed by Ofcom for poor customer service, saw its share price fall from 232.6p just after the markets opened to 231.3 by midday.
Around 2.5 million customers (38 per cent) say they experienced at least one major problem when trying to switch, while 70 per cent had some difficulty.
One of the biggest hurdles in changing provider is having to speak to the current provider, and facing unwanted attempts to persuade the customer to stay, Ofcom said.
Phone providers will have 18 months to comply with the regulations, so changes should come into effect by 1 July 2019.
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The current process sees those who want to transfer their number to a new network having to call their current provider to request a "porting authorisation code", and give this to the company they plan to join.
"For more than a decade Three has been encouraging Ofcom to do more to ensure that consumers can easily switch mobile phone provider and get the best deal", said a Three spokesperson. "While it's disappointing Ofcom did not go further, this is still an improvement that will make it easier for more customers to get a better deal".
Ready to get started? The PAC is valid for 30 days, and must be given to the new network to complete the switch. The new rules are aimed at speeding up the switch process for consumers and businesses.
However, while providers won't be able to charge during the notice period, they can still levy other fees, such as early repayment charges if you cancel and switch mid-contract. These changes will benefit the customer considerably; Ofcom estimates that this will save about £10m per year.
"For example, industry will need to set up the new short codes for people to text, and the means to send instant automated responses to switching requests, as well as new billing arrangements to end notice-period double payments", explained Ofcom.
"Proper provision also needs to be made for customers on 'bundled" packages, as well as those wanting to switch to forthcoming fibre-to-the-home (FTTH) broadband services'.