Hi Thierry,
This can be removed in Unity 5.x and 7.x and is related to the Subscribers COS;
Leaving messages: playing the "Record your message at the tone" prompt-You can indicate if you want Cisco Unity to tell callers to record their message after the tone.
Default: Cisco Unity plays the "Record your message at the tone" prompt after playing a subscriber or call handler greeting. Because some subscribers instruct callers when to record their messages in their greetings, callers hear the instruction twice. For this reason, you may want to specify that Cisco Unity does not play the prompt after some or all greetings when callers leave messages for particular subscribers or call handlers in your organization.
Scope: Individual subscribers and/or groups.
Enabling a Post-Greeting Recording
You can use the settings on the applicable Subscribers > Class of Service > Greetings page in the Cisco Unity Administrator to specify whether Cisco Unity plays a recording before allowing callers to leave a message for subscribers who are assigned to a class of service (COS).
When Cisco Unity is enabled to play a post-greeting recording, callers hear the recording immediately after a subscriber greeting, regardless of which personal greeting is enabled for the subscriber. By default, the post-greeting recording feature is disabled for all classes of service. A post-greeting recording does not play when:
The message recipient for a call handler is assigned to a distribution list.
Subscribers send, reply to, or forward messages to other subscribers, and when subscribers call a subscriber extension, log on to Cisco Unity during the subscriber greeting, and then leave a message.
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Note When you create a new COS based on an existing one, the new COS inherits the post-greeting recording settings but not the recording itself.
To Enable a Post-Greeting Recording for a Class of Service
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Step 1 In the Cisco Unity Administrator, go to the applicable Subscribers > Class of Service > Greetings page.
Step 2 In the After Greeting, Play Recording Before Taking Messages section, select one of the following options to enable the feature and indicate which callers will hear the recording:
Play Recording Only for Unidentified Callers-Before they leave a message, outside callers and subscribers who did not log on to Cisco Unity before calling from an external phone or from a phone that is not associated with a subscriber account hear the subscriber or call handler greeting and then the recording.
Play Recording to All Callers-Before they leave a message, subscribers and outside callers hear subscriber or call handler greeting and then the recording.
Step 3 Use the Media Master control bar to record what you want callers to hear, or specify an existing WAV file as the recording.
(You use the Copy/Paste From File options on the Options menu of the Media Master control bar to use a prerecorded WAV file as the recording.)
Step 4 Click the Save icon.
From this good doc;
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/administration/guide/ex/5xcusag150e.html#wp1047770
For Unity versions earlier than 5.0, you may be able to record short silent prompts and replace the two referenced by Jeff in this good thread;
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=Unified%20Communications%20Applications&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cbefa60
Hope this helps!
Rob
