Suppose you need to look at a Photon application running on some QNX machine other than the one with the modem you're connecting to. Not a problem. You can use the -n option to specify the full QNX pathname of any Photon session on that remote QNX network.
The phrelay program recognizes that you really want to be connected to a Photon on the second node, so it automatically migrates itself to that node, but continues to use the modem you dialed in on (i.e. the modem on the first node). Since QNX is an inherently distributed operating system, this happens seamlessly and efficiently.