Among the captured equipment was Iranian and Russian eavesdropping and jamming gear, some of it military grade. The Israelis believe that Hizbollah was also able to jam or decipher some messages made on their military radios (which use frequency hopping and encryption to prevent this.) But when Israeli troops get sloppy using their military radios, Hizbollah intel operatives, with the right skills and equipment, can listen in or jam.
Israeli troops had been warned not to use their cell phones along the border, but this was a difficult rule to enforce. That, in turn, makes it clear that the Israelis got sloppy with their intel, and counter-intelligence work. That is not unusual. It happens in every other nation, and for all of recorded history. It's called the "victory disease" for a militarily superior nation, and simply the "curse of peacetime" for any troops who have not been in combat for a while. Hizbollah took advantage of Israeli hubris and laxity. That said, the Israelis have shown an ability to get back in shape after they get their faces rubbed in their own shortcomings.
Israel captured many Hizbollah facilities during its recent war in Lebanon, along with many Hizbollah operatives. With all that, Israel learned a lot about Hizbollah intelligence gathering activities. Apparently, Hizbollah intel operations were more widespread and energetic than the Israelis thought. In addition to information collected electronically (like cell phone numbers of Israeli soldiers), there was apparently a network of spies within Israel. Most Arab-Israelis live in northern Israel, and some them appear to have been on Hizbollah's payroll.