Could you install the debug symbol packages and reproduce this bug again? Your crashlog is missing some important information to debug the problem.

Unfortunately, arch AFAIK do not provide debug packages for kde. It should be compiled from sources. Anyway I will try.

Here is a little more complete complete backtrace:

Application: KDE Daemon (kdeinit4), signal: Segmentation fault
[Current thread is 1 (Thread 0x7f674311b760 (LWP 1520))]

Thread 3 (Thread 0x7f672cbf7700 (LWP 1526)):
#0  0x00007f67407d8b83 in poll () from /lib/libc.so.6
#1  0x00007f673d8267d4 in ?? () from /usr/lib/libglib-2.0.so.0
#2  0x00007f673d826d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#3  0x00007f6741d9845e in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#4  0x00007f6741d6ca62 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#5  0x00007f6741d6cc67 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#6  0x00007f6741c8467f in QThread::exec() () from /usr/lib/libQtCore.so.4
#7  0x00007f6741d4fa9f in ?? () from /usr/lib/libQtCore.so.4
#8  0x00007f6741c870d5 in ?? () from /usr/lib/libQtCore.so.4
#9  0x00007f67419fdd60 in start_thread () from /lib/libpthread.so.0
#10 0x00007f67407e0e2d in clone () from /lib/libc.so.6
#11 0x0000000000000000 in ?? ()

Thread 2 (Thread 0x7f6724168700 (LWP 1571)):
#0  0x00007f67407d8b83 in poll () from /lib/libc.so.6
#1  0x00007f673d8267d4 in ?? () from /usr/lib/libglib-2.0.so.0
#2  0x00007f673d826d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#3  0x00007f6741d9845e in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#4  0x00007f6741d6ca62 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#5  0x00007f6741d6cc67 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#6  0x00007f6741c8467f in QThread::exec() () from /usr/lib/libQtCore.so.4
#7  0x00007f6741d4fa9f in ?? () from /usr/lib/libQtCore.so.4
#8  0x00007f6741c870d5 in ?? () from /usr/lib/libQtCore.so.4
#9  0x00007f67419fdd60 in start_thread () from /lib/libpthread.so.0
#10 0x00007f67407e0e2d in clone () from /lib/libc.so.6
#11 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f674311b760 (LWP 1520)):
[KCrash Handler]
#6  0x00007f6724eaf6b0 in Solid::Control::FrontendObjectPrivate::backendObject() const () from /usr/lib/libsolidcontrol.so.4
#7  0x00007f6724ebdbd5 in Solid::Control::ModemGsmCardInterface::sendPin(QString const&) const () from /usr/lib/libsolidcontrol.so.4
#8  0x00007f672577ff03 in NetworkInterfaceMonitor::requestPin(QString const&) () from /usr/lib/libknmservice.so.4
#9  0x00007f6725778a61 in NetworkInterfaceMonitor::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libknmservice.so.4
#10 0x00007f6741d803aa in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#11 0x00007f6724ebd1b5 in Solid::Control::ModemInterface::unlockRequiredChanged(QString const&) () from /usr/lib/libsolidcontrol.so.4
#12 0x00007f6724ebd351 in Solid::Control::ModemInterface::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libsolidcontrol.so.4
#13 0x00007f6724eaf180 in Solid::Control::ModemGsmCardInterface::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libsolidcontrol.so.4
#14 0x00007f6741d83f4e in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#15 0x00007f6740f2f194 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#16 0x00007f6740f34001 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#17 0x00007f6742b07226 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#18 0x00007f6741d6d86c in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#19 0x00007f6741d70bdf in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQtCore.so.4
#20 0x00007f6741d97f93 in ?? () from /usr/lib/libQtCore.so.4
#21 0x00007f673d82629d in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#22 0x00007f673d826a78 in ?? () from /usr/lib/libglib-2.0.so.0
#23 0x00007f673d826d09 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#24 0x00007f6741d983f6 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#25 0x00007f6740fd20ae in ?? () from /usr/lib/libQtGui.so.4
#26 0x00007f6741d6ca62 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#27 0x00007f6741d6cc67 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#28 0x00007f6741d70e5b in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#29 0x00007f6731b75ca5 in kdemain () from /usr/lib/libkdeinit4_kded4.so
#30 0x0000000000408102 in launch(int, char const*, char const*, char const*, int, char const*, bool, char const*, bool, char const*) ()
#31 0x000000000040574a in main ()

Which NetworkManager and ModemManager versions do you use? Also, could send me the NetworkManager and ModemManager logs? Usually the log messages are written to /var/log/messages or /var/log/daemong.log.

Created attachment 63031 [details]
Modem manager log

Created attachment 63032 [details]
NetworkManager log

(In reply to comment #4)
> Which NetworkManager and ModemManager versions do you use? Also, could send me
> the NetworkManager and ModemManager logs? Usually the log messages are written
> to /var/log/messages or /var/log/daemong.log.

I have attached the logs.
The versions are: 
0.5 for ModemManager
0.8.9997 for NetworkManager
The logs are saved during two attempts to send the pin (and two crashes).
Additionaly if I cancel sendpin, and try to connect using kde networkmanagement plasma applet (git20110726), commit=72f48aff1a672af24f66c26dd83b3ac6ee87df5f
(I have defined the pin) then i can connect, sometimes I need try twice, (I suppose it is because the long time to detect a valid apn).
Also i think that with kde 4.6.95 the error did not appear. It begun with an upgrade to kde 4.7.0

(In reply to comment #4)
> Which NetworkManager and ModemManager versions do you use? Also, could send me
> the NetworkManager and ModemManager logs? Usually the log messages are written
> to /var/log/messages or /var/log/daemong.log.

I have attached the logs.
The versions are: 
0.5 for ModemManager
0.8.9997 for NetworkManager
The logs are saved during two attempts to send the pin (and two crashes).
Additionaly if I cancel sendpin, and try to connect using kde networkmanagement plasma applet (git20110726), commit=72f48aff1a672af24f66c26dd83b3ac6ee87df5f
(I have defined the pin) then i can connect, sometimes I need try twice, (I suppose it is because the long time to detect a valid apn).
Also i think that with kde 4.6.95 the error did not appear. It begun with an upgrade to kde 4.7.0

I introduced a change in Solid's ModemManager backend from KDE SC 4.7.0 that changes binary compatibility, maybe that is what is causing your problem. But, that would only happen if you use kde-workspace < 4.7.0 with Plasma NM compiled against kde-workspace >= 4.7.0 (or vice-versa), that should not happen unless you are using outdated kde-workspace packages (Solid's MM backend is in kde-workspace repository).

I use 3G on a regular basis and have never had this kind of problem, but I use Gentoo and compile everything from source. Probably this is a problem with packages compiled against non-binary compatible libraries.

You are completely right Mr. Lamarque.
I have built the kde networkmanagement applet from sources, using Arch ABS.
I have installed the compiled version and now it works like a charm.
It seems that the binary Arch package was built prior to upgrade to kde 4.7.
I will file a bug to Arch.
Sorry for the inconvenience, I suppose this should be closed as not valid bug or so.
Thanks a lot for taking the time of reading the report.

I will close it as downstream because the real problem is how the packages are compiled. Sorry for this inconvinience, the change in Solid's ModemManager backend is necessary to implement reporting errors when trying to PIN unlock a GSM phone or modem. Without the change it is not possible to report errors and you could end up locking your PIN and needing the PUK to unlock it.

*** Bug 282009 has been marked as a duplicate of this bug. ***

*** Bug 306010 has been marked as a duplicate of this bug. ***