A fix for the 30 second voicemail problem some users experience with UK IP telephony providers. The problem is caused by the IP telephony provider not receiving any data from Asterisk while voicemails are recorded. The silence is interpreted as a connection failure and the call terminated. This patch is a workaround that transmits a periodic "hiss" to the caller while they are leaving a message. This was written for 1.0.5, but should work with newer versions.
Dowload the patch from: http://www.vipadia.com/freedownloads/ukvoicemail.tgz
To install, tar -xzf the distribution file, then:
cp silence.gsm /var/lib/asterisk/sounds/.
and in your asterisk source directory:
patch -p0 < generate_silence.diff
New versions of Asterisk should not need the patch - you can now cause the silence generation to happen with an option in asterisk.conf:
From README.asterisk.conf:
transmit_silence_during_record = yes | no ; send SLINEAR silence while channel is being recorded