I had a story a few months ago on Technobiography about some sensors temporarily installed at the Boni MRT station. I hypothesized that these were sensors would allow passage of commuters with the use of a cellphone. I wondered out loud whether the sensor would use SMS or bluetooth, or some other technology.
Later on, in private e-mails, I discovered more about the technology behind these mysterious sensors that appear and disappear at the Boni MRT station. Now, after trying out the EZ Link card in Singapore, I have a better understanding of how these sensors could work.