Transport for London is reported by the Independent to be close to reaching a deal with representatives from Nokia and O2 in order to produce a handset with a built-in Oyster card.
So you'd simply be able to swipe a compatible mobile phone across the Oystercard readers. The cost of the ticket would either be be added to the customer's monthly phone bill or deducted from a top-up account linked to the phone, similar to pay-as-you-go mobile phone services. The Register said it's "likely centre around the Nokia 6131-NFC handset, as that's the only model with the technology currently built in.
Oyster is based on Phillips' MiFare technology, otherwise known as ISO14443 Type A, which these days is a subset of NFC. So the Nokia handsets should already be compatible with the Oyster readers on the ticket gates."
If you're a Barclaycard customer you might have already been selected to trial this. As early next year several hundred Barclaycard customers will receive the Nokia handsets that will work in around 1,000 London shops - they need only to be waved at RFID reader terminals to carry out the transaction. Small payments go through instantly, while anything over ten quid requires a PIN.