Nitrogen Tanks to Keep the Internet Dry?

In a recent visit to New York, I ran into nitrogen tanks at several of the city corners. There are many guesses to why there are there and who put them there. The most common belief indicates that telecom companies uses them in the maintenance of cables and fiber bundles. For instance, Verizon seems to use the tanks to pump nitrogen gas into the phone lines to keep them dry. In any case, these tanks are great examples of unexpected protuberance on top of a city invisible infrastructure, very much similar to the painting at the crossroads, roads, and sidewalks revealing the underground networks. Yet another Sliding Friction moment.