Will switch for bus fare

Today's London edition of Metro has an ad from Orange offering GBP40 credit on an Oyster card (London's public transport smartcard system) for new contract customers signing up in-store. My casual observation is that a significant amount of cellular traffic in London is generated by people on their way home calling to say "I'm on the bus," or equally likely, "I'm on the bus and it's stuck in traffic/broken down." This could be a shrewd subterfuge by Orange to generate more outgoing minutes. More likely, and less tongue-in-cheek, is that consumers may perceive more value from a giveaway of an overpriced service (public transport), than a flashy handset or offers of more minutes.