In addition to credit cards, pre-paid giftcards and PayPal, the PlayStation Store and Sony Entertainment Network now support a "mobile billing" option for buying Hatsune Miku DLC, episodes of Teen Wolf, Music Unlimited subscriptions and whatever else the kids are into these days.
When adding funds to your virtual wallet through either the PS3's PlayStation Store or SEN's Account Management site, selecting the "Use Mobile" option will initiate the procedure. After receiving and confirming a text message (standard carrier rates apply, natch), the amount added to your wallet will either be tacked onto your phone bill, or deducted from your pre-paid phone account if that's how your plan swings.
We're still holding out for a poultry-based bartering system. How many chickens do you think Battlefield 4 DLC is going to cost?