See the commands with numbers at the end? phone1 is the phone number for modem 1 and so on. I' ve never used more than one modem so I' m not sure but " wireless-port" might let you define more than one wireless modem.
# config system modem
FGT80C3909642519 (modem) # set
*status enable/disable modem
pin-init AT command to set the PIN (use only once after reboot or change)
*mode set modem operation mode
auto-dial enable/disable auto-dial after a reboot or disconnection
dial-on-demand enable/disable dial-on-demand
idle-timer idle timer in minutes
redial redial limit: 1-10 attempts or none (redial forever)
holddown-timer hold down time in seconds. (1-60)
connect-timeout connection completion timeout: 30-255 seconds (default:90)
wireless-custom-vendor-id Vendor ID in hexadecimal format, 0000-ffff
wireless-custom-product-id Product ID in hexadecimal format, 0000-ffff
wireless-port wireless port, 0 for default, 1 for first port, ...
phone1 phone number 1
username1 user name 1
passwd1 password 1
extra-init1 extra initialization string to modem 1
peer-modem1 specify peer modem type for phone1
ppp-echo-request1 enable/disable PPP echo-request to modem 1
authtype1 set allowed authentication types for modem 1
phone2 phone number 2
username2 user name 2
passwd2 password 2
extra-init2 extra initialization string to modem 2
peer-modem2 specify peer modem type for phone2
ppp-echo-request2 enable/disable PPP echo-request to modem 2
authtype2 set allowed authentication types for modem 2
phone3 phone number 3
username3 user name 3
passwd3 password 3
extra-init3 extra initialization string to modem 3
peer-modem3 specify peer modem type for phone3
ppp-echo-request3 enable/disable PPP echo-request to modem 3
altmode enable/disable altmode
authtype3 set allowed authentication types for modem 3
distance distance of learned routes (1-255)
priority priority of learned routes (0-4294967295)