I recently discovered that using the IRDA hack to setup Bluetooth dial-up networking (as described in the ZUG Wiki) renders IRK unusable when the BT DUN connection is active. I guess I shouldn't be surprised (I'm sure the IRDA port is locked by the QTopia networking subsystem, even though the hacked /etc/ppp/peer file resuts in ppp connecting via an rfcomm port), but I was disappointed.
I am therefore happy to report that applying the same hack to a connection configured as "Dialup" solves this problem. (I have no idea what the default port for this type of connection is.) The connection is always available from the network applet (with the Socket 2.5 card, a BT-DUN connection is never available via the network applet), and having the connection active doesn't interfere with IRK!