To me iPhones are brilliant. They interface with our iPads etc I certainly wouldnt change now.
But they depend on the same network so if your signal from a provider is rubbish an iPhone wont help.
Jean and I both have iphones. Our supplier is 3 who we have been with for years and the signal locally is fine.
Our monthly cost are great. I pay £10 for unlimited calls and texts plus 8GB data which is more than enough mobile data for me. I mostly link to local wifi in pubs/restauramts etc etc if I am browsing. Jean just £6 for much less Data but fine for her usage profile.