If anyone interested, here my experiences with RB411GL and 3G USB modem ONDA MT833UP (provided with connector for optional external antenna).
Borad Name: RB411GL
RouterOS Version: 5.21[admin@MikroTik] /system resource usb> print
DEVICE VENDOR NAME SPEED
0 2:1 RB400 EHCI 480 Mbps
1 2:2 Onda MT833UP 480 Mbps
2 1:1 RB400 OHCI 12 Mbps
[admin@MikroTik] /system resource usb>[admin@MikroTik] > port print
Flags: I - inactiveNAME CHANNELS USED-BY BAUD-RATE
0 usb1 2 serial-terminal 9600
[admin@MikroTik] >[admin@MikroTik] /interface ppp-client> print detail
Flags: X - disabled, R - running
0 X name=“3G” max-mtu=1500 max-mru=1500 mrru=disabled port=usb1 data-channel=0 info-channel=0 apn=“ibox.tim.it” pin=“” user=“” password=“”
profile=default phone=“*99#” dial-command=“ATDT *99#” modem-init=“ATZ;AT+CGDCONT=1,“IP”,“ibox.tim.it”” null-modem=no dial-on-demand=no
add-default-route=yes use-peer-dns=yes keepalive-timeout=30 allow=pap,chap,mschap1,mschap2
[admin@MikroTik] /interface ppp-client>[admin@MikroTik] > sys serial-terminal usb1 channel=1
[Ctrl-A is the prefix key]
atz
OK
atio
Mx83.HW.B01
EAGLE_R1.5.5.3VCL314831ERROR