A cell phone signal led rescue crews to a hiker who had been missing for four days in a mountain ravine on Oahu.  The crews reached 26-year-old Jan Vankat, Sunday morning. He had told his family he was going to hike a trail above the Nuuanu Pali Wednesday.  His family reported him missing Friday and police began a search.  They were able to pinpoint the location of Vankat's cell phone in the mountains at about 9 a.m. Sunday.  A fire helicopter was dispatched and Vankat was found at 11:15 a.m. He was in serious, but stable condition wedged against a tree after falling about 100 yards on the town side of the Koolau Mountains.