In the early days of BBSing and chats (like ddial) the phone companies had some pretty high per minute charges on anything considered "long distance", but no line charges on things that were considered "local". Call packs were a pricing scheme that the phone company used to charge a higher monthly fee to expand your "local" coverage and thus eliminate per minute charges. BBS and chat users frequently signed up for these as it was then possible to leave yourself connected for hours without worry about mounting phone bills.
Some of the bigger chat boards actually got giant call packs for themselves and set up systems so that you would dial in on your modem, connect, then disconnect and the BBS would call you back and make the connection - thus riding for free on their call pack rather than on your per minute charges.
Of course, this rampant use of the phone system for very long connections (way in excess of voice call averages) both to post and to download files soon brought the phone company's attention around. This quickly lead to the elimination of call packs.
But it was cool for awhile.
Thanks. I never got into it that deep. Interesting workaround though.