[GreenKeys] Interesting modem for a teletype up on eBay

[Jim Haynes]

Yep, it's pretty obvious to build a modem into the Model 33, make it
originate-only for use as a time-sharing computer terminal.  I guess
you have to worry a little bit about noise from the machine getting
into the signal.

Teletype Corp. couldn't do such a thing itself because it was owned
by AT&T, and AT&T wanted to make you rent one of their hardwired modems.
Also they didn't approve of acoustic coupled modems at all, and at first
there was some good reason for that.  They felt a modem should work over
just about any telephone call you would make, and at first the quality
of circuits was such that some connections would be fairly bad.
Acoustic coupling was practical because the quality of voice circuits
rapidly improved, and because most of the computer connections were
fairly short distance anyway.