2016-06-13 23:43:33.472781 [WARNING] switch_core_codec.c:703 Codec L16 Exists but not at the desired implementation. 0hz 8000ms 20ch
2016-06-13 23:43:33.472781 [ERR] mod_gsmopen.cpp:161 rev 1.5.15b~64bit [0000000000000000|37     ][ERRORA  161  ][gsm01     ][-1, 0, 0] Can't load codec?
2016-06-13 23:43:33.472781 [ERR] mod_gsmopen.cpp:207 rev 1.5.15b~64bit [0000000000000000|37     ][ERRORA  207  ][gsm01     ][-1, 0, 0] gsmopen_codec FAILED
2016-06-13 23:43:33.472781 [ERR] mod_gsmopen.cpp:1057 rev 1.5.15b~64bit [0000000000000000|37     ][ERRORA  1057 ][gsm01     ][-1, 0, 0] Doh! no tech_init?
2016-06-13 23:43:33.472781 [NOTICE] mod_gsmopen.cpp:1058 Close Channel N/A [CS_NEW]
2016-06-13 23:43:33.472781 [ERR] switch_core_timer.c:117 Timer is not properly configured.
2016-06-13 23:43:33.472781 [ERR] switch_core_timer.c:117 Timer is not properly configured.

  <X-PRE-PROCESS cmd="set" data="global_codec_prefs=G729,OPUS,G722,PCMU,PCMA,GSM"/>
  <X-PRE-PROCESS cmd="set" data="outbound_codec_prefs=G729,OPUS,G722,PCMU,PCMA,GSM"/>

<extension name="gsmopen">
  <condition field="destination_number" expression="^(123456789)$">
    <action application="bridge" data="gsmopen/gsm01/$1"/>   
    <action application="hangup"/>
 </condition>
</extension>