There actually aren't anywhere close to 2000 tapes in Frasier's (Kelsey Grammer) cabinet. Each small section contains 12 tapes. There are 6 sections in each columns and 11 columns are completely full. The 12th column contains 4 sections and Frasier puts the "2000th" tape in the first slot in the 5th section. This means that in total, there are only 841 tapes in the cabinet.
There are multiple celebrity callers in this episode. Allison Janney plays Phyllis, who calls in with a description of her missing cat, Jennifer Jason Leigh is Estelle, who calls in with a question for Bill Gates about multi-lingual user inferface add-ons, Bobby Short is Warrern & calls in asking Gates asking if he needs to make a boot disk when installing XP as an upgrade, and finally Larry Gelbart (Joe) calls in explaining how he understands how Frasier (Kelsey Grammer) feels losing his tape as he lost a gold cuff link a few years ago and that if anyone finds it, he'd love to have it back.