A few weeks ago I wrote in I Still Feel Your Pain that service providers or enterprises implementing VoIP on converged networks will experience an erosion of benefits without the right management tools in the IPT enabled network.
One of my favorite, all time freebie tools is Ethereal, which I run on both my laptops for fieldwork, especially when deep trouble arises. First the confession: the first time an engineer told me that I had to sniff packets I wasn't amused--that was in 1999. Afterwards, I love doing this and if you can't guess why, then just think of what I've said before- "SERVICE COSTS MONEY" and besides, it's great fun finding those disruptive culprits and getting paid to do so.