If you're in public and standing still, don't take a phone call. It's that simple. All you're doing is holding those around you hostage to a one-sided conversation. We don't care about your fantasy football team, or your fungal foot infection. So, whether you're on the subway, or standing in line at a Subway, think before speaking.
Also, traveling under the Hudson River in a tunnel lends itself to some serious reception problems. While you yammer away about the fight you had with your boyfriend, whoever is on the receiving end of your diatribe will find the constant cutting in and out insufferable. There are no winners.