In my office here at the Slaptijack world headquarters, I have a cordless phone attached to a Linksys (née Sipura) SPA-2100. Thanks to the Visual Message Waiting Indicator (VMWI), I have a nice blinking LED whenever I have a voicemail waiting on my Asterisk server. Unfortunately, the Linksys SPA-2100 is also configured by default to issue a periodic half-ring whenever a message is waiting.

You can remove this half ring by setting the VMWI Ring Splash Len. in the appropriate User tab to 0. Notice I said "appropriate." The Linksys SPA-2100 supports two users.

If you are provisioning your ATAs via XML, the following snippet should do the trick for the main line:

<VMWI_Ring_Splash_Len_1_ ua="rw">0</VMWI_Ring_Splash_Len_1_>

This should have the affect of not ringing the phone when a message is waiting, but give users the option of changing it on their own.