Its a call to be present.
There is nothing inherently wrong with wearing headphones on the train, but ask yourself why you're doing it.
If you put on Headphones to keep people from talking to you, you're making the choice to opt out of the human experience.?Make that choice every day on a 45 minute commute and after only a week 7.5 hours where you've opted out of chance encounter, conversation, possibly meeting a new friend or partner. It might not be a bad idea to make the choice to NOT disconnect, actively choosing to engage in the world around us makes a huge difference in how we percieve it, and how it percieves us.
An experiment I'd suggest, if you're the type to default to using your phone as an idle activity:
Next time you're idle and get the urge to pull out your phone, instead look around you and find the most interesting thing you can see. Why is it interesting? Is there anything abnormal about it? Is it's place significant? Take that and note it in your mind, have a conversation with a coworker about it later. Then take note, how did this pointless conversation make me feel?
Being present by choice, especially if done often, will create chances to engage with the World, and its inhabitants.
The other day someone told me life was boring. Put the phone down, make more than the 2 meter cone you can see from around your phone visible, and you'll find the World has a lot of engagement to offer.