wife's sister had a problem with her reception when she was at home - [had gotten rid of her land-line] - so verizon installed a booster on her roof for her - problem solved
for mobile use, as already mentioned - ALL areas are NOT always served - used to spend a lot of time traveling in my business - think at one time i had like almost a dozen different carriers and their phones - but i DID find spots that i couldn't even get one to work!!!
ps:
speaking of tunnels - my lg with verizon - i could talk ALL the way through the harbor tunel on 1-95 in baltimore, md - only dropped to 3 bars