ModemManager integration is organized as follows:


Common source
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 * nm-modem.[h|c]:
      Defines the basic `NMModem' object. The core NetworkManager implementation
      will use this interface exclusively, regardless of the real final type of
      the modem object.

 * nm-modem-manager.[h|c]:
      Defines the `NMModemManager' object, which takes care of listening to
      signals from the DBus inteface notifying about added or removed modems.
      It also takes care of creating proper `NMModem' objects from the
      information retrieved from the DBus interface.


ModemManager 0.7 integration
********************************************************************************

 * nm-modem-broadband.[h|c]:
      Defines the `NMModemBroadband' object, which is a subclass of `NMModem'.
      This object handles both 3GPP and 3GPP2 modems exposed in the new
      `ModemManager1' interface.


ModemManager 0.4/0.5/0.6 integration
********************************************************************************

 * nm-modem-types.h:
      Defines helper types to use with the (old) ModemManager DBus API.

 * nm-modem-generic.[h|c]:
      Defines the `NMModemGeneric' object. All modem objects based on the old
      ModemManager interface are subclasses of this one.

 * nm-modem-gsm.[h|c]:
      Defines the `NMModemGsm' object, which is a subclass of `NMModemGeneric'.
      This object handles 3GPP-specific (GSM, UMTS, HSPA, LTE) modems.

 * nm-modem-cdma.[h|c]:
      Defines the `NMModemCdma' object, which is a subclass of `NMModemGeneric'.
      This object handles 3GPP2-specific modems (CDMA, EV-DO).