Faced with persistent customer demand for wifi service on the train, Caltrain has hired a marketing firm to seek sponsorship for onboard wifi, according to the San Francisco Chronicle.

Caltrain researched the technology and found that it would take $3 million to equip the trains with wifi. Caltrain now seeking corporate sponsorships from companies such as Google.

This blogger thinks that one interesting potential sponsor would be Facebook. The Menlo Park-based social networking giant is piloting a program where users get free wifi service in exchange to posting a “checkin” to Facebook. Wouldn’t it be cool if you could “check in” to train #312? The Facebook pilot includes an “opt-out” feature that lets you check in without telling your friends where you are, in case you actually aren’t supposed to be going to the Giants game that afternoon.

About a year ago, Friends of Caltrain encouraged riders to let Caltrain know if they wanted wifi. In response, over 500 riders urged Caltrain to invest in wifi. Since then, wifi has been the single most common search term used in the Friends of Caltrain blog. Tech-savvy Caltrain riders are eager to be able to use wifi on the train, so that time on the train is more productive or relaxing, and the train is a better alternative to driving.