Update of status. Successfully connect usb 3g modem via otg cable to due and communicate to it using adapted cdcacm driver from usb host shield. Came to "CONECT" from provider but no further. Send PPP LCP packet completely same as sniffed from computer conversation and got no answer. There is 3 possible problems.
1. Problem with OTG cable. Same USB modem have problems when used on computer with 2m usb extend cable. No problem when connected directly. On due try modem with 2 different otg cable, same result.
2. Couldn't find any useful information about passing from AT commands to data communication (chat to ppp). Do I have to do something special. On computer serial port is reopened on that moment, probably for changing speed. Here I don't set any speed at all and speed is unimportant for my goal.
3. Something is missing, maybe some power to modem. There is procedure from getting "CONNECT". First due needs one minute to start communicating with modem on usb and after that modem do not respond to any AT command. Press reset button on due. After another minute modem respond to AT commands, but to ATDT... it responds with "NO CARRIER" indefinitely. Press reset button on due. Another minute of waiting and got "CONNECT" but nothing else after that. More resets gives me "NO CARRIER".