*CLI> module show
Module                         Description                              Use Count
res_features.so                Call Features Resource                   0
res_adsi.so                    ADSI Resource (not optional)             0
res_musiconhold.so             Music On Hold Resource                   0
chan_sip.so                    Session Initiation Protocol (SIP)        0
chan_iax2.so                   Inter Asterisk eXchange (Ver 2)          0
pbx_config.so                  Text Extension Configuration             0
app_dial.so                    Dialing Application                      0
app_directory.so               Extension Directory                      0
app_playback.so                Sound File Playback Application          0
app_voicemail.so               Comedian Mail (Voicemail System)         0
app_meetme.so                  MeetMe conference bridge                 0
app_page.so                    Page Multiple Phones                     0
app_dumpchan.so                Dump Info About The Calling Channel      0
codec_ulaw.so                  mu-Law Coder/Decoder                     0
codec_alaw.so                  A-law Coder/Decoder                      0
codec_a_mu.so                  A-law and Mulaw direct Coder/Decoder     0
codec_g726.so                  ITU G.726-32kbps G726 Transcoder         0
func_language.so               Channel language dialplan function       0
func_callerid.so               Caller ID related dialplan function      0
func_channel.so                Channel information dialplan function    0
format_wav.so                  Microsoft WAV format (8000Hz Signed Line 0
format_pcm.so                  Raw/Sun uLaw/ALaw 8KHz Audio support (PC 0
format_g726.so                 Raw G.726 (16/24/32/40kbps) data         0
format_g723.so                 G.723.1 Simple Timestamp File Format     0
24 modules loaded
*CLI> module unload app_playback.so
  == Unregistered application 'Playback'
*CLI> module show
Module                         Description                              Use Count
res_features.so                Call Features Resource                   0
res_adsi.so                    ADSI Resource (not optional)             0
res_musiconhold.so             Music On Hold Resource                   0
chan_sip.so                    Session Initiation Protocol (SIP)        0
chan_iax2.so                   Inter Asterisk eXchange (Ver 2)          0
pbx_config.so                  Text Extension Configuration             0
app_dial.so                    Dialing Application                      0
app_directory.so               Extension Directory                      0
app_playback.so                Sound File Playback Application          0
app_voicemail.so               Comedian Mail (Voicemail System)         0
app_meetme.so                  MeetMe conference bridge                 0
app_page.so                    Page Multiple Phones                     0
app_dumpchan.so                Dump Info About The Calling Channel      0
codec_ulaw.so                  mu-Law Coder/Decoder                     0
codec_alaw.so                  A-law Coder/Decoder                      0
codec_a_mu.so                  A-law and Mulaw direct Coder/Decoder     0
codec_g726.so                  ITU G.726-32kbps G726 Transcoder         0
func_language.so               Channel language dialplan function       0
func_callerid.so               Caller ID related dialplan function      0
func_channel.so                Channel information dialplan function    0
format_wav.so                  Microsoft WAV format (8000Hz Signed Line 0
format_pcm.so                  Raw/Sun uLaw/ALaw 8KHz Audio support (PC 0
format_g726.so                 Raw G.726 (16/24/32/40kbps) data         0
format_g723.so                 G.723.1 Simple Timestamp File Format     0
24 modules loaded
*CLI>


why app_playback is still around?