When a modem like a Sierra EM7355 (or any MBIM-capable Gobi modem) exposes CDMA capabilities, MM tries to enable the 3GPP2 interface and fails because MBIM doesn't handle CDMA yet.

[/dev/cdc-wdm1] Device capabilities retrieved:
	      Device type: 'embedded'
	   Cellular class: 'gsm, cdma'
	      Voice class: 'no-voice'
	        Sim class: 'removable'
	       Data class: 'gprs, edge, umts, hsdpa, hsupa, 1xrtt, 1xevdo, 1xevdo-reva'
	         SMS caps: 'pdu-receive, pdu-send'
	        Ctrl caps: 'reg-manual, cdma-mobile-ip, cdma-simple-ip, multi-carrier'
	     Max sessions: '8'
	Custom data class: 'unknown'
	        Device ID: 'xxxxx'
	    Firmware info: 'SWI9X15C_05.05'
	    Hardware info: 'EM7355'

[/dev/cdc-wdm1] Registration status:
	         Network error: 'unknown'
	        Register state: 'deregistered'
	         Register mode: 'automatic'
	Available data classes: 'unknown'
	Current cellular class: 'cdma'
	           Provider ID: 'unknown'
	         Provider name: 'unknown'
	          Roaming text: 'unknown'
	    Registration flags: 'packet-service-automatic-attach'

[/dev/cdc-wdm1] Registration status:
	         Network error: 'unknown'
	        Register state: 'searching'
	         Register mode: 'automatic'
	Available data classes: 'unknown'
	Current cellular class: 'gsm'
	           Provider ID: 'unknown'
	         Provider name: 'unknown'
	          Roaming text: 'unknown'
	    Registration flags: 'packet-service-automatic-attach'

mmcli -m 0 -e:
error: couldn't enable the modem: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Connected: No AT port available to run command'

ModemManager[4421]: [/dev/cdc-wdm1] Sent message (translated)...
<<<<<< Header:
<<<<<<   length      = 48
<<<<<<   type        = command (0x00000003)
<<<<<<   transaction = 18
<<<<<< Fragment header:
<<<<<<   total   = 1
<<<<<<   current = 0
<<<<<< Contents:
<<<<<<   service = 'basic-connect' (a289cc33-bcbb-8b4f-b6b0-133ec2aae6df)
<<<<<<   cid     = 'register-state' (0x00000009)
<<<<<<   type    = 'query' (0x00000000)
ModemManager[4421]: [/dev/cdc-wdm1] Received message...
>>>>>> RAW:
>>>>>>   length = 96
>>>>>>   data   = 03:00:00:80:60:00:00:00:12:00:00:00:01:00:00:00:00:00:00:00:A2:89:CC:33:BC:BB:8B:4F:B6:B0:13:3E:C2:AA:E6:DF:09:00:00:00:00:00:00:00:30:00:00:00:00:00:00:00:02:00:00:00:01:00:00:00:00:00:00:00:01:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:02:00:00:00
ModemManager[4421]: [/dev/cdc-wdm1] Received message (translated)...
>>>>>> Header:
>>>>>>   length      = 96
>>>>>>   type        = command-done (0x80000003)
>>>>>>   transaction = 18
>>>>>> Fragment header:
>>>>>>   total   = 1
>>>>>>   current = 0
>>>>>> Contents:
>>>>>>   status error = 'None' (0x00000000)
>>>>>>   service      = 'basic-connect' (a289cc33-bcbb-8b4f-b6b0-133ec2aae6df)
>>>>>>   cid          = 'register-state' (0x00000009)
ModemManager[4421]: <debug> [1436977958.922412] [mm-broadband-modem.c:8529] enabling_step(): Modem has CDMA capabilities, enabling the Modem CDMA interface...
ModemManager[4421]: <debug> [1436977958.922521] [mm-iface-modem-cdma.c:946] mm_iface_modem_cdma_run_registration_checks(): Running registration checks (CDMA1x: 'yes', EV-DO: 'yes')
ModemManager[4421]: <debug> [1436977958.922575] [mm-broadband-modem.c:7033] setup_registration_checks_context_complete_and_free(): Will skip all QCDM-based registration checks
ModemManager[4421]: <debug> [1436977958.922619] [mm-broadband-modem.c:7054] setup_registration_checks_context_complete_and_free(): Will skip generic detailed registration check, we don't have Sprint commands
ModemManager[4421]: <debug> [1436977958.922687] [mm-iface-modem-cdma.c:768] registration_check_step(): Starting QCDM-based registration checks
ModemManager[4421]: <debug> [1436977958.922732] [mm-iface-modem-cdma.c:780] registration_check_step():   Skipping all QCDM-based checks and falling back to AT-based checks
ModemManager[4421]: <debug> [1436977958.922772] [mm-iface-modem-cdma.c:823] registration_check_step(): Starting AT-based registration checks
ModemManager[4421]: <warn>  [1436977958.922841] [mm-iface-modem-cdma.c:641] get_service_status_ready(): Could not get service status: No AT port available to run command
ModemManager[4421]: <info>  [1436977958.922935] [mm-iface-modem.c:1203] __iface_modem_update_state_internal(): Modem /org/freedesktop/ModemManager1/Modem/0: state changed (enabling -> disabled)