A quick reworked example of how to get information from the ModemManager component of NetworkManager into python in a meaningful way.

ModemManager_Extraction.py

import sys
import dbus

from gi.repository import GObject

from pprint import pprint

# from gi.repository import GLib, GObject, Gio, ModemManager

bus = dbus.SystemBus()

manager_proxy = bus.get_object('org.freedesktop.ModemManager1', '/org/freedesktop/ModemManager1')
manager_iface = dbus.Interface(manager_proxy, dbus_interface='org.freedesktop.ModemManager1')
manager_om = dbus.Interface(manager_proxy, "org.freedesktop.DBus.ObjectManager")

#modems = manager_iface.EnumerateDevices()
modems = manager_om.GetManagedObjects()
if len(modems) == 0:
    print("No modems found")
    sys.exit(1)

#proxy = bus.get_object('org.freedesktop.ModemManager1', modems[0])
modem_proxy = bus.get_object('org.freedesktop.ModemManager1', '/org/freedesktop/ModemManager1/Modem/0')
modem = dbus.Interface(modem_proxy, dbus_interface='org.freedesktop.ModemManager1.Modem')
modem.Enable(True)
#modem.Enable(True)

messaging_iface = dbus.Interface(manager_proxy, dbus_interface='org.freedesktop.ModemManager.Modem.Messaging')
messaging_om = dbus.Interface(manager_proxy, "org.freedesktop.DBus.ObjectManager")
messaging_props = messaging_om.GetManagedObjects()

sms_iface = dbus.Interface(manager_proxy, dbus_interface='org.freedesktop.ModemManager1.Modem.Sms')
SMS_om = dbus.Interface(manager_proxy, "org.freedesktop.DBus.ObjectManager")
SMSs = SMS_om.GetManagedObjects()

pprint(SMSs['/org/freedesktop/ModemManager1/Modem/0']['org.freedesktop.ModemManager1.Modem.Messaging']['Messages'])

for sms_path in SMSs['/org/freedesktop/ModemManager1/Modem/0']['org.freedesktop.ModemManager1.Modem.Messaging']['Messages']:
	print('Reading SMS: ' + sms_path)
	sms_composite_path = sms_path
	sms_msg_proxy = bus.get_object('org.freedesktop.ModemManager1', sms_composite_path)
	#text_prop = sms_msg_proxy.Get('org.freedesktop.ModemManager1.Sms', 'Text', dbus_interface='org.freedesktop.DBus.Properties')
	#print(text_prop)
	text_props = sms_msg_proxy.GetAll('org.freedesktop.ModemManager1.Sms', dbus_interface='org.freedesktop.DBus.Properties')
	#print(text_props)
	print('Text from: ' + text_props['Number'])
	print('Text command: ' + text_props['Text'])
	print('Text At: ' + text_props['Timestamp'])