Q: iPhone 6 question

Hello. I have an iPhone 6 and service through Verizon. Over the last several months (10 months), my phone, on occasion states "no service." I'm not sure why. It doesn't matter where I'm at - home, work, or somewhere in between. The only way I can use the phone is on wifi when this happens. I have contacted Verizon times two and they have replaced the phone as well as the SIM card - not at the same time. It works fine for a while - then up to 3 hours of saying no service. My husband has an iPhone 5S and has no problems with it. He has verizon as well. When my son is home, his iPhone 6 works fine - he does, on a very rare occasion have issues saying no service, but maybe 2-3 minutes, max. Any suggestions? Thanks, in advance.