Looks like they are all at it:-
Trusted partners
O2 said that the limited sharing of numbers was "standard industry practice".
In a statement Everything Everywhere confirmed: "When Orange and T-Mobile customers use their mobile phones for general web browsing no customer information, such as mobile phone numbers, is shared with the website.
"As is the case with all mobile operators in the UK, Orange and T-Mobile customers can visit a small number of trusted partner websites where transactions can take place, such as purchasing ringtones. In order to complete the purchase or download customers pay via their Orange and T-Mobile accounts and hence mobile phone numbers have to be made available to these sites."
In a statement Vodafone said it pursued a similar policy adding that it only shared numbers with approved Vodafone UK partners who were "subject to security checks to ensure they conform to our stringent requirements around protecting our customers' privacy".
From BBC Website
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