1.- dmesg: 
asterisk[15735]: segfault at 40 ip 00007f317444b140 sp 00007f316aecc950 error 4 in chan_unistim.so[7f317443d000+23000]
asterisk[24099]: segfault at 40 ip 00007f8ead5f2140 sp 00007f8e5ff82950 error 4 in chan_unistim.so[7f8ead5e4000+23000]
asterisk[1406]: segfault at 40 ip 00007f31ed81e140 sp 00007f31e4223950 error 4 in chan_unistim.so[7f31ed810000+23000]
asterisk[6983]: segfault at 40 ip 00007fe332ea1140 sp 00007fe32982a950 error 4 in chan_unistim.so[7fe332e93000+23000]
asterisk[9815]: segfault at 40 ip 00007f1e82c7918d sp 00007f1e796fa950 error 4 in chan_unistim.so[7f1e82c6b000+23000]
asterisk[10608]: segfault at 40 ip 00007f205581e140 sp 00007f204c29f950 error 4 in chan_unistim.so[7f2055810000+23000]
asterisk[28726]: segfault at 7f9a00000009 ip 00007f9aaefc36c1 sp 00007f9a496945e0 error 4 in libc-2.12.so[7f9aaef4b000+18b000]
asterisk[30046]: segfault at 3 ip 000000000044e876 sp 00007f0d71e46ad0 error 4 in asterisk[400000+232000]
asterisk[30276]: segfault at 40 ip 00007f12d085b18d sp 00007f12c72dc950 error 4 in chan_unistim.so[7f12d084d000+23000]
2.- tail -f /var/log/messages
Dec 27 11:06:10 localhost kernel: asterisk[1406]: segfault at 40 ip 00007f31ed81e140 sp 00007f31e4223950 error 4 in chan_unistim.so[7f31ed810000+23000]
Dec 27 11:34:53 localhost kernel: asterisk[6983]: segfault at 40 ip 00007fe332ea1140 sp 00007fe32982a950 error 4 in chan_unistim.so[7fe332e93000+23000]
Dec 27 11:41:56 localhost kernel: asterisk[9815]: segfault at 40 ip 00007f1e82c7918d sp 00007f1e796fa950 error 4 in chan_unistim.so[7f1e82c6b000+23000]
Dec 27 13:59:31 localhost kernel: asterisk[10608]: segfault at 40 ip 00007f205581e140 sp 00007f204c29f950 error 4 in chan_unistim.so[7f2055810000+23000]
Dec 27 14:51:52 localhost kernel: asterisk[28726]: segfault at 7f9a00000009 ip 00007f9aaefc36c1 sp 00007f9a496945e0 error 4 in libc-2.12.so[7f9aaef4b000+18b000]
Dec 27 15:05:30 localhost kernel: asterisk[30046]: segfault at 3 ip 000000000044e876 sp 00007f0d71e46ad0 error 4 in asterisk[400000+232000]
Dec 27 15:47:10 localhost kernel: asterisk[30276]: segfault at 40 ip 00007f12d085b18d sp 00007f12c72dc950 error 4 in chan_unistim.so[7f12d084d000+23000]
3.- The problem seems when transfering calls (sometimes only)
4.- Asterisk Log, last reboot
[2013-12-26 11:30:55] VERBOSE[2603][C-00000028] app_dial.c: – Called USTM/321@XXXXX
[2013-12-26 11:30:55] VERBOSE[2603][C-00000028] app_dial.c: – USTM/321@XXXXX-0x7fee2000ca30 is ringing
[2013-12-26 11:31:02] VERBOSE[2603][C-00000028] app_dial.c: – USTM/321@XXXXX-0x7fee2000ca30 answered DAHDI/2-1
[2013-12-26 11:31:09] VERBOSE[1795] res_musiconhold.c: – Started music on hold, class 'default', on DAHDI/2-1
[2013-12-26 11:31:10] VERBOSE[2670] chan_unistim.c: – Starting switch on '321@XXXXX-0' to 331
[2013-12-26 11:31:10] VERBOSE[2670][C-00000029] pbx.c: – Executing [331@from-internal:1] Dial("USTM/321@XXXXX-0x7fee140542b0", "USTM/331@YYYYY") in new stack
[2013-12-26 11:31:10] VERBOSE[2670][C-00000029] app_dial.c: – Called USTM/331@YYYYY
[2013-12-26 11:31:10] NOTICE[2670][C-00000029] chan_unistim.c: Connected party is now YYYYY <331>
[2013-12-26 11:31:10] VERBOSE[2670][C-00000029] app_dial.c: – USTM/331@YYYYY-0x7fee28018b70 is ringing
[2013-12-26 11:31:10] WARNING[2603][C-00000028] chan_unistim.c: RTP handle NULL while reading on subchannel 2
[2013-12-26 11:31:12] VERBOSE[1795] res_musiconhold.c: – Stopped music on hold on DAHDI/2-1
[2013-12-26 11:31:12] NOTICE[1795] chan_unistim.c: UNISTIM transfer: trying to masquerade DAHDI/2-1 into USTM/321@XXXXX-0x7fee140542b0
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [h@macro-dial-one:1] Macro("USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>", "hangupcall,") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:1] GotoIf("USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>", "1?theend") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Goto (macro-hangupcall,s,3)
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:3] ExecIf("USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>", "0?Set(CDR(recordingfile)=)") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:4] Hangup("USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>", "") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-hangupcall, s, 4) exited non-zero on 'USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>' in macro 'hangupcall'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: == Spawn extension (macro-dial-one, h, 1) exited non-zero on 'USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-dial-one, s, 42) exited non-zero on 'USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>' in macro 'dial-one'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-exten-vm, s, 16) exited non-zero on 'USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>' in macro 'exten-vm'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: == Spawn extension (from-did-direct, 321, 2) exited non-zero on 'USTM/321@XXXXX-0x7fee140542b0<ZOMBIE>'
[2013-12-26 11:31:12] VERBOSE[2670][C-00000029] app_dial.c: – USTM/331@YYYYY-0x7fee28018b70 answered DAHDI/2-1
[2013-12-26 11:31:16] VERBOSE[1731] asterisk.c: – Remote UNIX connection
[2013-12-26 11:31:16] VERBOSE[2776] asterisk.c: Beginning asterisk shutdown....
[2013-12-26 11:31:16] VERBOSE[2670][C-00000029] pbx.c: – Executing [h@from-internal:1] Hangup("DAHDI/2-1", "") in new stack
5.- Other Information
[2013-12-26 11:31:10] VERBOSE[2670][C-00000029] app_dial.c: – Called USTM/331@YYYY
[2013-12-26 11:31:10] NOTICE[2670][C-00000029] chan_unistim.c: Connected party is now YYYY <331>
[2013-12-26 11:31:10] VERBOSE[2670][C-00000029] app_dial.c: – USTM/331@YYYY-0x7fee28018b70 is ringing
[2013-12-26 11:31:10] WARNING[2603][C-00000028] chan_unistim.c: RTP handle NULL while reading on subchannel 2
[2013-12-26 11:31:12] VERBOSE[1795] res_musiconhold.c: – Stopped music on hold on DAHDI/2-1
[2013-12-26 11:31:12] NOTICE[1795] chan_unistim.c: UNISTIM transfer: trying to masquerade DAHDI/2-1 into USTM/321@XXXX-0x7fee140542b0
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [h@macro-dial-one:1] Macro("USTM/321@XXXX-0x7fee140542b0<ZOMBIE>", "hangupcall,") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:1] GotoIf("USTM/321@XXXX-0x7fee140542b0<ZOMBIE>", "1?theend") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Goto (macro-hangupcall,s,3)
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:3] ExecIf("USTM/321@XXXX-0x7fee140542b0<ZOMBIE>", "0?Set(CDR(recordingfile)=)") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: – Executing [s@macro-hangupcall:4] Hangup("USTM/321@XXXX-0x7fee140542b0<ZOMBIE>", "") in new stack
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-hangupcall, s, 4) exited non-zero on 'USTM/321@XXXX-0x7fee140542b0<ZOMBIE>' in macro 'hangupcall'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: == Spawn extension (macro-dial-one, h, 1) exited non-zero on 'USTM/321@XXXX-0x7fee140542b0<ZOMBIE>'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-dial-one, s, 42) exited non-zero on 'USTM/321@XXXX-0x7fee140542b0<ZOMBIE>' in macro 'dial-one'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] app_macro.c: == Spawn extension (macro-exten-vm, s, 16) exited non-zero on 'USTM/321@XXXX-0x7fee140542b0<ZOMBIE>' in macro 'exten-vm'
[2013-12-26 11:31:12] VERBOSE[2603][C-00000028] pbx.c: == Spawn extension (from-did-direct, 321, 2) exited non-zero on 'USTM/321@XXXX-0x7fee140542b0<ZOMBIE>'
[2013-12-26 11:31:12] VERBOSE[2670][C-00000029] app_dial.c: – USTM/331@YYYY-0x7fee28018b70 answered DAHDI/2-1
[2013-12-26 11:31:16] VERBOSE[1731] asterisk.c: – Remote UNIX connection
[2013-12-26 11:31:16] VERBOSE[2776] asterisk.c: Beginning asterisk shutdown....