sockets - Manage serial port from two processes simultaneosly -

i have following scenario:

• rasperry pi connected device via serial port
• 3g dongle connected raspberry (with ability make/recieve calls)
• one process reading data serial port , redirecting server (using 3g)
• another process waiting incoming call, , when calls program takes data serial port , redirect via 3g dongle using @ commands ( fax-call). when calls, call made using @ commands , caller should able "speak" final device connected serial port.

the problem 2 processes can not live since using same serial port, , when 1 process started, other can not read data serial (port busy).

is there way achieve ? can make "fake" serial port, or redirects data?

thank much

you may write single service communicates real serial port offers 2 virtual serial ports described here virtual serial port linux