It works! I've done some connection to internet with Ericcson T18 phone and DI27 irda modem. After the correct kernel configurations, you need only these commands:
modprobe ircomm
irmanager -d 1
pon
Probably the modprobe is not necessary, but you MUST activate the autoprobe in the irmanager (with -d 1) if you don't want the carrier lost after few seconds. You need the correct scripts in /etc/chatscripts, /etc/ppp/peers and /etc/ppp.