Swapped home buttons, now phones won’t connect with AT&T

I have two iPhone 4 devices, and two phone numbers. The home button on the phone I use more often (phone 1) was going bad. Yes, I should have just swapped the SIM cards but I didn’t. I swapped the home buttons instead. It went exactly as expected (the good home button, from phone 2, works great on phone 1, and the lousy home button works just as badly on phone 2 as it used to on phone 1). BUT now neither phone will connect with the cell carrier (AT&T). Phone 2 connected with AT&T weakly (one bar) for a few seconds when first powered up after the swap but nothing since). Both phones alternate saying (upper left) “searching….” and “no service.” I tried swapping SIM cards, resetting network settings, toggling airplane mode and cell data, and updating iOS on phone 1. Nothing. Any ideas/guidance much appreciated.