If there is problem for cellular connection. Please check below points:

Do you order the model with cellular option

Make sure you order the model with cellular option. Can check by command:

root@dragino-1bbd90:~# lsusb
Bus 001 Device 004: ID 2c7c:0125      --> This is the Cellular module
Bus 001 Device 002: ID 1a40:0101 Terminus Technology Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Do you input the SIM card correctly

Below command can check:

root@dragino-1bbd90:~# comgt -d /dev/ttyUSB3
SIM ready
Waiting for Registration..(120 sec max)
Registered on Home network: "CHN-CT",7
Signal Quality: 23,99

Check dialing info

Fri Feb  7 01:20:28 2020 daemon.notice pppd[29452]: pppd 2.4.7 started by root, uid 0
Fri Feb  7 01:20:29 2020 user.notice iot_keep_alive: Ping WAN
Fri Feb  7 01:20:29 2020 user.notice iot_keep_alive: Default interface is
Fri Feb  7 01:20:29 2020 user.notice iot_keep_alive: No internet at any interface
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: abort on (BUSY)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: abort on (NO CARRIER)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: abort on (ERROR)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: report (CONNECT)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: timeout set to 10 seconds
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: send (AT&F^M)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: expect (OK)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: AT&F^M^M
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: OK
Fri Feb  7 01:20:29 2020 local2.info chat[29485]:  -- got it
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: send (ATE1^M)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: expect (OK)
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: ^M
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: ATE1^M^M
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: OK
Fri Feb  7 01:20:29 2020 local2.info chat[29485]:  -- got it
Fri Feb  7 01:20:29 2020 local2.info chat[29485]: send (AT+CGDCONT=1,"IP",""^M)
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: timeout set to 30 seconds
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: expect (OK)
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: ^M
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: AT+CGDCONT=1,"IP",""^M^M
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: OK
Fri Feb  7 01:20:30 2020 local2.info chat[29485]:  -- got it
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: send (ATD*99#^M)      -----> In case the dialling process already reach here. Normally problem is with provider, need to check if the SIM card has balance or other requirement from cellular operator
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: expect (CONNECT)
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: ^M
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: ATD*99#^M^M
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: CONNECT
Fri Feb  7 01:20:30 2020 local2.info chat[29485]:  -- got it
Fri Feb  7 01:20:30 2020 local2.info chat[29485]: send ( ^M)
Fri Feb  7 01:20:30 2020 daemon.info pppd[29452]: Serial connection established.