The story in which Puck finds Kurt's phone (on a bench?) and idly goes through it, eventually checking the call listing; seeing a number Kurt called often, Puck calls it thinking it's a sex hot-line but finds out it's actually a help-line. He confronts Kurt about it (the next day) when he returns the phone.
That's all I got. >.< Help?
ETA: Found by a wonderful nonny mouse! It's Not Yet by huntershotmymom.