(gdb) bt
#0  0x0809a921 in ast_bridged_channel (chan=0x0) at channel.c:4120
#1  0xb7a2e7b1 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
#2  0xb7a31678 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
#3  0xb7a32242 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
#4  0xb7a31bc0 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
#5  0x080e855b in ast_io_wait (ioc=0x822d4b8, howlong=1000) at io.c:287
#6  0xb7a335cb in ?? () from /usr/lib/asterisk/modules/chan_sip.so
#7  0x08166cba in dummy_start (data=0x8287f58) at utils.c:1024
#8  0xb7ca3315 in start_thread () from /lib/i686/libpthread.so.0
#9  0xb7d91dde in clone () from /lib/i686/libc.so.6

(gdb) bt full
#0  0x0809a921 in ast_bridged_channel (chan=0x0) at channel.c:4120
        bridged = (struct ast_channel *) 0xb7a585e8
#1  0xb7a2e7b1 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
No locals.
#2  0xb7a31678 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
No locals.
#3  0xb7a32242 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
No locals.
#4  0xb7a31bc0 in ?? () from /usr/lib/asterisk/modules/chan_sip.so
No locals.
#5  0x080e855b in ast_io_wait (ioc=0x822d4b8, howlong=1000) at io.c:287
        res = 1
        x = 0
        origcnt = 1
#6  0xb7a335cb in ?? () from /usr/lib/asterisk/modules/chan_sip.so
No locals.
#7  0x08166cba in dummy_start (data=0x8287f58) at utils.c:1024
        __cancel_buf = {__cancel_jmp_buf = {{__cancel_jmp_buf = {-1211424780, 0, 4001536, -1214827592, -1631999656, -1677174745}, __mask_was_saved = 0}}, __pad = {
    0xb7973480, 0x0, 0x0, 0x0}}
        __cancel_routine = (void (*)(void *)) 0x806f894 <ast_unregister_thread>
        __cancel_arg = (void *) 0xb7973b90
        not_first_call = 0
        ret = (void *) 0x0
        a = {start_routine = 0xb7a33340, data = 0x0, name = 0x822f620 "do_monitor", ' ' <repeats 11 times>, "started at [19540] chan_sip.c restart_monitor()"}
        lock_info = (struct thr_lock_info *) 0x8248f00
        mutex_attr = {__size = "\001\000\000", __align = 1}
#8  0xb7ca3315 in start_thread () from /lib/i686/libpthread.so.0
No symbol table info available.
#9  0xb7d91dde in clone () from /lib/i686/libc.so.6
No symbol table info available.