[snip]
#0  0x08080fde in ast_write (chan=0xb7b27ec8, fr=0xb7b628f8) at channel.c:2807
2807                    if (chan->tech->write == NULL)
(gdb) bt
#0  0x08080fde in ast_write (chan=0xb7b27ec8, fr=0xb7b628f8) at channel.c:2807
#1  0x0805856a in jb_get_and_deliver (chan=0xb7b27ec8) at abstract_jb.c:405
#2  0x08058420 in ast_jb_get_and_deliver (c0=0xb7b27ec8, c1=0x98320e0) at abstract_jb.c:374
#3  0x080846b3 in ast_generic_bridge (c0=0xb7b27ec8, c1=0x98320e0, config=0x72c23c0, fo=0x72c221c, rc=0x72c2218, bridge_end=
      {tv_sec = 0, tv_usec = 0}) at channel.c:3922
#4  0x080857bb in ast_channel_bridge (c0=0xb7b27ec8, c1=0x98320e0, config=0x72c23c0, fo=0x72c221c, rc=0x72c2218)
    at channel.c:4235
#5  0x0017e456 in ast_bridge_call (chan=0xb7b27ec8, peer=0x98320e0, config=0x72c23c0) at res_features.c:1421
#6  0x007c72cf in dial_exec_full (chan=0xb7b27ec8, data=0x72c7000, peerflags=0x72c2e10, continue_exec=0x0) at app_dial.c:1651
#7  0x007c755c in dial_exec (chan=0xb7b27ec8, data=0x72c7000) at app_dial.c:1705
#8  0x080b637f in pbx_exec (c=0xb7b27ec8, app=0x97c0ed8, data=0x72c7000) at pbx.c:532
#9  0x080b95c5 in pbx_extension_helper (c=0xb7b27ec8, con=0x0, context=0xb7b28048 "sub-huntgroup", exten=0xb7b28098 "ringall", 
    priority=25, label=0x0, callerid=0xb7dd6970 "9549280282", action=E_SPAWN) at pbx.c:1833
#10 0x080ba687 in ast_spawn_extension (c=0xb7b27ec8, context=0xb7b28048 "sub-huntgroup", exten=0xb7b28098 "ringall", 
    priority=25, callerid=0xb7dd6970 "9549280282") at pbx.c:2288
#11 0x080bab75 in __ast_pbx_run (c=0xb7b27ec8) at pbx.c:2388
#12 0x080bb872 in pbx_thread (data=0xb7b27ec8) at pbx.c:2601
#13 0x080f3f95 in dummy_start (data=0xb7dd8348) at utils.c:545
#14 0x008a8371 in start_thread () from /lib/tls/libpthread.so.0
#15 0x005f6ffe in clone () from /lib/tls/libc.so.6
(gdb) bt full
#0  0x08080fde in ast_write (chan=0xb7b27ec8, fr=0xb7b628f8) at channel.c:2807
        res = -1
        f = (struct ast_frame *) 0x0
        __PRETTY_FUNCTION__ = "ast_write"
#1  0x0805856a in jb_get_and_deliver (chan=0xb7b27ec8) at abstract_jb.c:405
        jb = (struct ast_jb *) 0xb7b28264
        jbimpl = (struct ast_jb_impl *) 0x81468e0
        jbobj = (void *) 0x97d9290
        f = (struct ast_frame *) 0xb7b628f8
        finterp = {frametype = 159224464, subclass = 0, datalen = 120331832, samples = 134581448, mallocd = 1032, 
  mallocd_hdr_len = 0, offset = 120331504, src = 0x0, data = 0x97d9290, delivery = {tv_sec = 0, tv_usec = 0}, frame_list = {
    next = 0x10}, has_timing_info = 8, ts = 8, len = 2, seqno = 0}
        now = 371645
        interpolation_len = 20
        res = 0
        __PRETTY_FUNCTION__ = "jb_get_and_deliver"
#2  0x08058420 in ast_jb_get_and_deliver (c0=0xb7b27ec8, c1=0x98320e0) at abstract_jb.c:374
        jb0 = (struct ast_jb *) 0xb7b28264
        jb1 = (struct ast_jb *) 0x983247c
        c0_use_jb = 1
        c0_jb_is_created = 4
        c1_use_jb = 1
        c1_jb_is_created = 4
#3  0x080846b3 in ast_generic_bridge (c0=0xb7b27ec8, c1=0x98320e0, config=0x72c23c0, fo=0x72c221c, rc=0x72c2218, bridge_end=
      {tv_sec = 0, tv_usec = 0}) at channel.c:3922
        who = (struct ast_channel *) 0x0
        other = (struct ast_channel *) 0xb7b27ec8
        cs = {0xb7b27ec8, 0x98320e0, 0x98320e0}
        f = (struct ast_frame *) 0x981615c
        res = AST_BRIDGE_COMPLETE
        o0nativeformats = 4
        o1nativeformats = 4
        watch_c0_dtmf = 0
        watch_c1_dtmf = 0
        pvt0 = (void *) 0xb7b13198
        pvt1 = (void *) 0x97ff1b8
        frame_put_in_jb = 1
        jb_in_use = 1
        to = 0
(gdb) print chan
$1 = (struct ast_channel *) 0xb7b27ec8
(gdb) print chan->tech
$2 = (const struct ast_channel_tech *) 0x7b9380
(gdb) print chan->tech->write
$3 = (int (* const)(struct ast_channel *, struct ast_frame *)) 0xdfc3