good luck because linux support for irda sucks. i've been trying to connect my nokia 6600 using the ma-620 dongle for a while, but i couldn't find a clear enough howto.
anyway here's what i do, so you can get as far as i am, maybe someone can help us both:
1- log into root using 'su -'
[rayyes@gateless ~]$ su -
2- make sure the dongle is unplugged, then plug it in and type 'dmesg'
pl2303 2-1:1.0: PL-2303 converter detected
usb 2-1: PL-2303 converter now attached to ttyUSB2
this is important because the last few lines of dmesg will tell you which port the dongle connected to (add /dev/ to the tty it connects to, in this case its /dev/ttyUSB2) .
3-now you can use irattach (i use ma600 since 620 is not there):
[root@gateless ~]# irattach /dev/ttyUSB2 -d ma600 -s
4- now if you type 'irdadump' you can see the info being passed back and forth, in my case, FC3 identifies the remote device as Nokia 6600:
22:05:48.526539 xid:cmd b86d92c0 > ffffffff S=6 s=4 (14)
22:05:48.526567 xid:cmd 934b8024 > ffffffff S=6 s=4 (14)
22:05:48.605522 xid:rsp 934b8024 < 57be4106 S=6 s=4 Nokia 6600 hint=9225 [ PDA/Palmtop Modem Telephony IrCOMM IrOBEX ] (27)
at this point everything gets hazy, and blurry and my legs become really really heavy, then i wake up but the nightmare won't go away