The default logic to decide which are the current capabilities parses outputs of several commands, including +GCAP. The "+CGSM" reply in +GCAP is used to say a device is "gsm-umts", although this doesn't seem to be right; a 4G-only 3GPP modem will also reply +CGSM.


E.g.:

$ mmcli -m 0

/org/freedesktop/ModemManager1/Modem/0 (device id '13d738ce72d62749f86308b7d620f063dd38bc47')
  -------------------------
  Hardware |   manufacturer: 'Telit'
           |          model: 'LE866-SV1'
           |       revision: '23.00.002 (M0A.00020)'
           |      supported: 'gsm-umts, lte'
           |        current: 'gsm-umts, lte'
           |   equipment id: '352613070042357'


Logs show how the AT+WS46? check does report 4G-only as supported *mode*, but still, we report 'gsm-umts' capability, which would apply only to 3GPP 2G/3G devices.

 (ttyUSB0): --> 'AT+GCAP<CR>'
 (ttyUSB0): <-- '<CR><LF>'
 (ttyUSB0): <-- '+GCAP'
 (ttyUSB0): <-- ': +CG'
 (ttyUSB0): <-- 'SM,+DS'
 (ttyUSB0): <-- ',+FCLA'
 (ttyUSB0): <-- 'SS,+MS'
 (ttyUSB0): <-- ',+ES'
 (ttyUSB0): <-- '<CR><LF>'
 (ttyUSB0): <-- '<CR><LF>OK<CR>'
 (ttyUSB0): <-- '<LF>'
 (ttyUSB0): --> 'AT+WS46=?<CR>'
 (ttyUSB0): <-- '<CR><LF>'
 (ttyUSB0): <-- '+WS46:'
 (ttyUSB0): <-- ' (28)'
 (ttyUSB0): <-- '<CR><LF>'
 (ttyUSB0): <-- '<CR><LF>OK<CR><LF>'
  loaded current capabilities: gsm-umts, lte