Do any of your modems support the Command: Yn - Long Space Disconnect any more?

Yes, the MT5600BA and MT5600BR but not the MT5600BA-V92.

Command: Yn Long Space Disconnect

Values: n = 0 or 1

Default: 0

Description:

Y0 Disables sending/responding to a long space break signal on disconnect.

Y1 Enables long space disconnect. In non-error correction mode, the modem sends a