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I go all over the US for work and vacation, and when I do I like to see how the local network homes on various tandems (AT&T, MCI, Sprint) when I can. I like to do it from landlines and cellphones since both route differently. I also do this with VOIP carriers since often times they dump you on the POTS network at various places, and this can either be static or dynamic. (Can you say Tandem round robin?) Often times calls from landline, cellular or VOIP go to the newer "edge switches" that are in the format of NPA-xL (like 412-9L). I believe most of these are 5ESS based. But most of the time you can reach a 4ESS in the format of xxx-T. Anyhow, I was in a very rural place in Wyoming in May while on vacation. It was a rest stop in the middle of nowhere. The rest stop used to have a pay phone (you can tell it was there and removed), but they did have a microcell for Verizon Wireless (obviously fed by DSL). Doing my test for AT&T, it did the round robin as I suspected (some sort of VOIP backhaul) and I came up on 088-T a few times. That *used* to be the AT&T tandem for San Diego. They retired the 4ESS a few years ago, but now it comes up in the "new" voice that AT&T is using for the new generation "N4E" system.The N4E uses the old 4ESS software hosted in a virtual environment in newer hardware (lot smaller footprint and more in tune with modern packet switching). Sure enough, I was in San Diego last week and tried it from a COCOT. Yup, they do have a new N4E and has the new voice on the trailer. So I'm wondering how many of the existing 4ESS systems will be replaced by N4E systems? I also wonder how many 4ESS and N4E systems are out there. I found a N4E in Scottsdale, AZ (NPA 480) not too long ago. Haven't explored what else is new out there recently.