ZTE 3G module not responding to picocom about picocom HOT 5 CLOSED

Probably not a picocom issue. I leave it open in case somebody can help

perhabs you should try /dev/ttyUSB1 or higher. Many usb 3G modems use different 
device files for Data and AT control commands.

[deleted comment]

I made some partial progress, using picocom "-i" option (no port init), but 
this is what I get if I simply type A + T + Z + <enter> afters starting 
picocom: 

root@android:/ # picocom -i -f h -b 115200  /dev/ttyUSB3     
picocom v1.6

port is        : /dev/ttyUSB3
flowcontrol    : RTS/CTS
baudrate is    : 115200
parity is      : none
databits are   : 8
escape is      : C-a
local echo is  : no
noinit is      : yes
noreset is     : no
nolock is      : no
send_cmd is    : sz -vv
receive_cmd is : rz -vv
imap is        :
omap is        :
emap is        : crcrlf,delbs,

Terminal ready
AAAAAAAAAAAAAAAAAAATATATATATATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZATZA
TZATZATZATZATZATZATZATZATZ

ERROR

ATZ


OK

ATZ


OK

ATZ


OK 

Single characters, as well as the entire command are repeated several times. 
But, at least I get the 'OK' back, sometimes. What could be happening here? Any 
idea?