I've found the solution.
New-CsAnnouncement –Parent <service of Application Server running the Announcement application, in the form: service:ApplicationServer:<fqdn>
> `
-Name <unique name to be used as destination in unassigned number table> `
[-AudioFilePrompt <FileName specified in Import-CsAnnouncementFile>] `
[-TextToSpeechPrompt <text string to be converted to speech>] `
[-Language <Language for playing the TTS prompt (required for PromptTts)>] `
[-TargetUri sip:SIPAddress for transferring caller after announcement]
New-CsAnnouncement -Identity ApplicationServer:lyncpool.your.domain -Name "Unassigned" -TargetUri "sip:+412312332123@your.domain;user=phone"