can't connect with 3g internal modem using network-manager

I have an internal sierra 3g modem in my dell laptop

Manufacturer: Sierra Wireless, Inc.
Model: MC8790
Revision: K1_0_2_18AP C:/WS/FW/K1_0_2_18AP/MSM6290/SRC 2008/12/29 14:49:54

The network manager correctly detects the modem and seems to initialize it. but when I try to connect it gives up saying "NO CARRIER".

I tried with wvdial, and the modem works like a charm, so I tried to track down where the problem is. Probably there is some AT command missing somewere but without luck. The mess of layers between network-manager, udev, modem-manager screwed me up, also because modem-manager is completely undocumented and seems to don't have any configuration file. Also, I could not find anywhere how to manually set options in the system connections for network manager.

But triying to debug the situation I discovered that opening a minicom session to the modem command port and simply entering a reset (ATZ) solves the issue and after that the network manager connects successfully.

Maybe someone help in finding a solution for this problem?

The software versions are

ii modemmanager 0.5.2.0-0ubunt D-Bus service for managing modems
ii network-manage 0.9.4.0-0ubunt network management framework (daemon and use
LSB Version: core-2.0-ia32:core-2.0-noarch:core-3.0-ia32:core-3.0-noarch:core-3.1-ia32:core-3.1-noarch:core-3.2-ia32:core-3.2-noarch:core-4.0-ia32:core-4.0-noarch

Francesco

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: modemmanager 0.5.2.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-24.39-generic-pae 3.2.16
Uname: Linux 3.2.0-24-generic-pae i686
ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
Date: Mon May 28 10:08:21 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release i386 (20120423)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: modemmanager
UpgradeStatus: No upgrade log present (probably fresh install)