Yes, but there is our embedded ascii based communication protocol, where CRLF is used to msg end indication and as I found, in b4a it is not identical when working only with text - like line ends. So I prefer this way and to manually add CR and LF chars to end of message.Note that if you are sending text and cannot use prefix mode then you can still use AsyncStreamsText class. It will collect and split the message based on the end of line characters.
Thanks, but i don't know how to discover wich process/driver (and how to use other ports)This means that this port is already opened by a different process / driver.
COM3 is often reserved for modem connection (old telephone line, RJ11 port). Maybe you will find it in your Device Manager > Modems.
Have you created a new COM port under Bluetooth settings ?
You can have a look at this page http://www.flightprep.com/rootpage.php?page=w7btsetup (see step 10).