You should be more specific in your question, as phreaking covers a HUGE range now. Not to mention such a large portion of it is either "dead" for most people or hard to do(i mean where the hell do you even FIND a payphone in the US any more?). If your talking more along the lines of VOIP phreaking their is occasionally some discussion here about that kind of thing, but really its not talked about much (here). id say your best over all resources for that would be phrack and 2600. As they still relatively regularly have some sort of article on phreaking as that is what they started as. If your looking for more old school stuff, obviously those would also be great places to start. if you just want to start a more general discussion or have a specific question then id say start a thread about it.