I have an iPhone 7 128 GB on Verizon network, and I am experiencing the same frustrating problem as well. It seems to happen more (or at least I recognize it more) when I am driving and using GPS. However every area where I live (and I have never had any signal drop on my iPhone 6), I am consistently getting dropped signals and in random places on my iPhone 7. Even in my home where I've always had a strong signal, I am continually getting dropped off the network. At first when it started to happen, I was able to go into airplane mode and turn it off and then on again. This seem to correct the problem, when it came back on the network for a short time, however, now I have to reset my phone every time it happens.
I have reset all settings, I have reinstalled the OS, I have even performed a DFU upgrade, and reinserted the SIM card after cleaning it, none of this helps.
Apple needs to resolve this quickly, because I use my phone for work and if I cannot receive signals this is of no use for me.