...when AOL decides that they don't want his Jabber server talking with AIM and start blocking him on their end.
[link|http://www.acronymfinder.com/af-query.asp?String=exact&Acronym=AIUI&Find=Find|AIUI], the message you type (supposing you're using the AIM interface) goes from your machine to Peter's guildenstern to the AIM server to your intended non-IWETHEY recipient who is theoretically not using Peter's Jabber server. If AOL steps in the middle there and stops messages from Guildenstern being sent, then, well, it doesn't matter if Peter adds in AIM support on his end.