Both my wife and I have AT&T model iPhone 5S' that are unlocked. We have lived in our apartment for a year and a half with no real connection issues. Usually get 2-3 bars of LTE, no dropped calls, texts are fine, ect. We got our phones on 10/10/13, and are on AT&T but thinking about switching to T-Mobile so I got a T-Mobile SIM and have been using it off and on to see how the connections are around here. Starting last Friday, we were both on AT&T, and started getting No Service displayed. I put my T-Mobile SIM in, and the connection is about the same as AT&T usually is with 2-3 bars of LTE. No connection drops, calls go through fine, texts fine, ect. Put the AT&T SIM back in, and it cycles in about 3-5 minute long periods where it will display LTE, LTE goes away, No Service, Searching, LTE, no LTE, No Service, Searching....so forth and so on with a loop of dropping the connection, comes back, drops...all day and night. But as soon as we leave the apartment and hit the road the connection is fine. I was able to tether off my wife's phone fine. Thinking it might be WIFI interference or something I unplugged every WIFI/radio capable device in our apartment and no change. I have a friend who lives in another building in the same complex and he has not had any issues with his AT&T phone. I did two AT&T tech support chats today, and during the first one we did restores, reset network settings, she updated their info for IMEI's, all to no change in the looping of the connection. She ended up blaming the phones. I doubt its the phones because we have two which have been perfectly fine until Friday night, and they both work fine with the T-Mobile SIM. On Saturday we got a new SIM for my wife's phone. Was fine out and about. Come home, and the same thing starts again. So a SIM change on one of the phones had no affect. I did a second tech support chat, and he ended up submitting a network support ticket. Gave me a case number. I don't think its really a network issue unless our specific apartment suddenly developed a dead spot, and nowhere else. The ONLY thing that seems slightly plausible is we think someone 'might' have moved into the apartment next to us last week, and 'might' have some sort of radio setup like a HAM or CB. I have no reason to know if they have a radio like that of some sort. We only started hearing a dog bark we never have heard before, and then banging like someone nailing a bunch of stuff up. Usually what people do when they move in somewhere, and we noticed a new WIFI SSID we haven't seen before. But its not effecting T-Mobile, and 4G and LTE and Edge all run on different frequencies, right? I doubt a radio running on a set frequency could cause enough interference it would cut the connection down to where we are seeing this but only on AT&T. Not even cutting out just LTE, and only the phone only getting 4G. Neither phone can maintain a connection on AT&T for more than a few minutes no matter what type of connection. Just cycles through the same way on 4G. Once that i saw, the phone went from LTE to 4G to E(dge) to GRPS and then No Service. Another reason its not the phones is because as soon as we leave they are completely fine. Like it's isolated to the general vicinity of our apartment...but as mentioned I unplugged everything, and there was no change in the situation. Its not anything in our apartment causing it. We've lived here for a year and half with no connection issues. We've been on AT&T since they bought out Cingular, and never really had a connection problem at all besides maybe some rural area with no stops for 50 miles. If I didn't get the T-Mobile SIM...both of our phones would be unusable at home besides WIFI stuff..but we can't maintain a call, texts fail to send multiple times, ect. But this really has me intrigued. We'd still have to stick with AT&T for another year anyways until our contract is out...so just perm switching to T-Mobile right now is not a long term option. Just was curious about the service they have around here so I got the $30 Wal Mart 100min/UNL/UNL plan to test for a month. Anyone have any ideas? Possible new neighbor possibly having some sort of radio thats generating interference seem plausible? What about the cell signal boosters AT&T sells you plug into an ethernet port? Do those cause problems for other AT&T phones NOT getting a signal from that device but still trying to get a signal from the tower? Any other ideas? If I can't figure this out we're join to be hurting before too long. My wife has had to use Skype to call her mom and anyone else she's needed to call from home, and I ordered another T-Mobile nano SIM today just in case. If we can't figure it out by the time it gets here we're gonna get her a month of the 100/UNL/UNL Walmart plans, and I really don't like the idea of paying two carriers at once...one of which we can't even use at home. I have the ticket through AT&T but if its something like a radio or a cell signal booster then what? Not like I can search someone else's apartment or even make them get rid of something like that.