A device or provider is using a codec which AskoziaPBX is unable to transcode. Not all of the selectable codecs in AskoziaPBX are transcodable due either to licensing issues or processing power.
This message means that “silence suppression” is enabled on a client but it is not fully supported in Asterisk 1.4. It is a harmless message, but turning off “silence suppression” or “transmit silence” in your SIP client will make it go away. For some background info, see Comfort Noise or Voice Activity Detection
A harmless message about some optional functionality not being enabled.
A SIP client is attempting to subscribe / monitor the account's voicemail messages. This feature is not yet implemented in AskoziaPBX as voicemails are sent per e-mail. This request can be disabled in the SIP client but is a harmless message and can be safely ignored.