iPhone 11pro max, used for 1 yr and 3 months, problem happens on 12/26. same problem. lost signal, no service. I checked with carrier, no issues, put the SIM card in another phone, the SIM is working. put other SIM in this 11promax, no service, no signal. called the apple support. restart, reset network settings, airplane on/off, restore the phone to factory settings, restore the phone with PC/iTunes. same issue. Contacted with the Apple support tech agent, three different senior tech agents, a support tech manager (that agent said he is the manager, and he is the highest level manager in Apple, the agent hang up my call at the end)，they run the diagnostic check on the phone as well. they cannot found any issues, cannot explain why this issue happened , and said it may because of a hardware issues... then they provided me the only repair solution for this phone which is to replace the phone with cost of $880+taxes. still contacting with Apple support team, another manager start working on my case now, we did a conference call with my SIM carrier and now it’s waiting on a tech ticket number from SIM carrier. fingers crossed...