Sony has partnered with the mobile payment system Boku to present an easy way to buy digital products and manage your PSN wallet. Basically, this allows you to add your mobile number into the Boku system and confirm payments via SMS -- it'll then be added to your bill automatically. Look for the "mobile" option when adding to your wallet, UK PSN users.
Sony of Europe's Gordon Thornton explains, "We are always looking at new ways to give our customers more choice in terms of content, accessibility and payment methods, and are pleased to be able to offer the option of mobile operator billing, which are becoming more and more popular."
That works for me, honestly. Sony is finally catching up with Microsoft's Xbox.com and the ease of buying content, and it looks like everything will be in place with the PS4 rolls around. Currently, this system is only in place in the UK.