JSI Tip 4645. How do I control the speaker volume, or shut it off?

You can use Control Panel / Phone and Modem to add a user initialization string to the modem's Properties:

The following command controls the modem speaker volume when the speaker is turned on.   L0 : Selects the lowest speaker volume.  L1 : Selects a low speaker volume.  L2 : Selects medium speaker volume.  L3 : Selects high speaker volume. Mn : (Speaker Control)    This command selects when the modem speaker will be on or off. M0 : The speaker is always off. M1 : Enables the speaker during call establishment, but off after the carrier is detected. M2 : The speaker is always on. M3 : Disables the speaker during the dialing period and receiving carrier, but on during answering.

I prefer to do it in the register. The modem entry on all my PC's is at HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlClass\{4D36E96D-E325-11CE-BFC1-08002BE10318}000. I add add/modify the UserInit string value. To turn off the modem speaker, I enter M0.