From Homestar Runner Wiki
Sometimes a character will use a disconnected telephone, or a telephone handset with frayed wires poking out of the bottom. It is uncertain whether the telephones actually work with phone service, as Coach Z was talking to his mother/father with one in Homestar Presents: Presents. This is probably not the case, however, because Coach Z is known to do odd things. Some evidence that the phones have some function appears in the Strong Bad Email replacement where Strong Bad uses it to page The Cheat despite the phone's lack of connectivity. There are no buttons on these phones, which would suggest that they are corded phones and the bases would have the buttons.
On a related note, Coach Z attempted to speak on a drawing of a cell phone on a notepad in diorama.
- Email 50 emails — tan phone (possibly a goof)
- Email replacement — red phone, with spiral cord
- Strong Bad is in Jail Cartoon — tin can "Eww" phone in end segment
- Homestar Presents: Presents — red phone
- Email modeling — yellow phone
- Email rock opera — tan phone (same as in 50 emails)
- Email geddup noise — green phone (with and without cord)
- Email isp — yellow phone
- Marzipan's Answering Machine Version 14.2 — green phone in Easter egg
- Email pizza joint — yellow phone
- In addition, the commentary mentions the running gag.
- Twenty THANXty Six — While pretending to be a "Top Exec", Stinkoman shouts into a disconnected phone.