Swapper: someone with whom you trade software with.
Contact: a person with whom you make contact for swapping, joining a group, etc. Also, a person who was able to obtain software not yet released (ie, an insider from software companies, magazines, etc.) for the purpose of releasing to the scene by said group. Or someone who might be able to become a part of a given group (coder, cracker, musician, gfx artist, etc.)
Call our boards: each crack group typically had at least
one bulletin board, and most of the better groups had several of them. Their invite to call the boards (which, for the most part, no longer exist) is so that you can upload (or download) more pirated software or become a courier (spread software from one board to the next), or if you are a contact
supposed to call them. Back in the day when those messages were created, they were calling out to others within their elite circle. But today, these messages are just nostalgic remnants of the past (at least on Amiga games, demos, readme files).
Edit: Deej beat me to it!