How about using the modemDemo sample application which will have the offline option?
root@swi-mdm9x28-wp:~# app runProc modemDemo1 send --exe=send – 1234567 “Sim”
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cat /legato/systems/current/appsWriteable/modemDemo1/smsC
hat.txt
SIM 1 is inserted and unlocked. ICCID=8985200012741552068 IMSI=454003074155206
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cm data
Index: 1
APN: hkcsl
PDP Type: IPV4V6
Connected: no
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# app runProc modemDemo1 send --exe=send – 1234567 "Online
"
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cat /legato/systems/current/appsWriteable/modemDemo1/smsC
hat.txt
SIM 1 is inserted and unlocked. ICCID=8985200012741552068 IMSI=454003074155206
Requesting data connection.
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cm data
Index: 1
APN: hkcsl
PDP Type: IPV4V6
Connected: yes
Interface: rmnet_data0
Family[IPv4]: inet
IP[IPv4]: 10.128.167.61
Gateway[IPv4]: 10.128.167.62
Dns1[IPv4]: 10.145.148.1
Dns2[IPv4]: 10.144.148.133
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# ping www.google.com
PING www.google.com (172.217.26.132): 56 data bytes
64 bytes from 172.217.26.132: seq=0 ttl=59 time=16.461 ms
64 bytes from 172.217.26.132: seq=1 ttl=59 time=26.180 ms
^C
— www.google.com ping statistics —
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 16.461/21.320/26.180 ms
root@swi-mdm9x28-wp:~# app runProc modemDemo1 send --exe=send – 1234567 “Offlin
e”
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cat /legato/systems/current/appsWriteable/modemDemo1/smsC
hat.txt
SIM 1 is inserted and unlocked. ICCID=8985200012741552068 IMSI=454003074155206
Requesting data connection.
Releasing data connection.
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# ping www.google.com
ping: bad address ‘www.google.com’
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# app runProc modemDemo1 send --exe=send – 1234567 "Online
"
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# ping www.google.com
PING www.google.com (172.217.26.132): 56 data bytes
64 bytes from 172.217.26.132: seq=0 ttl=59 time=19.727 ms
64 bytes from 172.217.26.132: seq=1 ttl=59 time=18.251 ms
^C
— www.google.com ping statistics —
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 18.251/18.989/19.727 ms
root@swi-mdm9x28-wp:~# cat /legato/systems/current/appsWriteable/modemDemo1/smsC
hat.txt
SIM 1 is inserted and unlocked. ICCID=8985200012741552068 IMSI=454003074155206
Requesting data connection.
Releasing data connection.
Requesting data connection.
root@swi-mdm9x28-wp:~#
root@swi-mdm9x28-wp:~# cm info
Device: WP7607
IMEI: 359779081234565
IMEISV: 6
FSN: VN730485080103
Firmware Version: SWI9X07Y_02.28.03.03 000000 jenki[ 374.277531] i2c-msm-v2 78b8000.i2c: NACK: slave not responding, ensure its powered: msgs(n:1 cur:0 tx) bc(rx:0 tx:2) mode:FIFO slv_addr:0x3a MSTR_STS:0x0c1300c8 OPER:0x00000090
ns 2019/05/21 03:33:04
Bootloader Version: SWI9X07Y_[ 374.297141] i2c-msm-v2 78b8000.i2c: NACK: slave not responding, ensure its powered: msgs(n:1 cur:0 tx) bc(rx:0 tx:2) mode:FIFO slv_addr:0x3a MSTR_STS:0x0c1300c8 OPER:0x00000090
02.28.03.03 000000 jenkins 2019/05/21 03:33:04
MCU Version: 002.011
PRI Part Number (PN): 9908958
PRI Revision: 001.000
Carrier PRI Name: GENERIC
Carrier PRI Revision: 002.068_000
SKU: 1104301
Last Reset Cause: Crash
Resets Count: Expected: 195 Unexpected: 16