Modem to send/receive faxes

[ml-vic]

I'm trying to send faxes by means of a bluetooth connection between my PC and 
my cell phone. 
Because hylafax needs a modem that is a serial port to send/receive faxes I 
tried and succeded with

rfcomm_sppd -a my_BT_ADDR  -t /dev/ttyp3

and, as requested by hylafax,  I was able to connect to it

cu -l ttyp3

But I was unable to send any AT command thru it.

Could someone out there clarify this point to this almost absolute beginner 
suggesting, step by step what I shall do? 

Ciao
Vittorio