It's takes a while for Lionel to realize that whenever he has a crap day, he gets a call from Mr. Glasses. They're usually on the "detective we need a favor" line, or a follow-up on a case, but sometimes they just talk. Etc. and so on.

Open to any interpretation of the subject line and if it's Finch/Fusco friendship, affection or smut is totally up to the filler!