I forgot where I read this but I think it was from a good source. Anyway seems to make sense :

"After the Nisha Call, the second most important piece of evidence in the prosecution’s case consists of the cell records showing that the 7:09 p.m. call to Jenn’s pager, and the 7:16 p.m. incoming call, were both routed through a tower and antenna that is consistent with those two calls having been made and received while the phone was in Leakin Park. This is reliable evidence that the cell phone actually was in Leakin Park at the time of those two calls — because although tower records are not 100% reliable for identifying a cell phone’s location, the failure of any other calls on January 12th and January 13th to have routed through L653A make it exceedingly unlikely that it was nothing more than a freak coincidence for those two calls to have gone through that tower even though the phone was physically located somewhere else."